Two Short, Sound, Simple Proofs that Muhammad Was a False Prophet
"But the prophet who speaks a word presumptuously in My name which I have
not commanded him to speak . . . that prophet shall die."
GOD (Deuteronomy18:20) 
"I have fabricated things against God and have imputed to Him words which He has not spoken."
MUHAMMAD (Al-Tabari 6:111) 
Muhammad claimed that Jewish and Christian scriptures had predicted his coming (see, e.g., Qur’an 7:157). This has led Muslim apologists to comb the Old and New Testaments in search of passages that refer to their prophet. While all biblical evidence offered by Muslims in support of their prophet appears horribly strained to non-Muslims (provided the latter read the passages in context) and has been thoroughly refuted time and again, it is still common to hear Muslims claim that the Bible speaks about Muhammad.
The most popular "prophecy" about Muhammad is found in Deuteronomy 18. It is quite ironic, then, to learn that, according to Deuteronomy 18, Muhammad can’t possibly be a prophet. As we will see, this puts Muslims in an awkward position, and helps show the lengths to which they will go in their efforts to defend their prophet.
The purpose of this essay is to prove, based on Muslim claims (including their appeal to Deuteronomy 18), that Muhammad was a false prophet. We will presente two arguments against the prophethood of Muhammad, and we will carefully defende the arguments. Once shown that the arguments are sound, we will briefly discuss the options available to Muslims who want to reject the obvious conclusion.
I. THE DEUTERONOMY DEDUCTIONS
There are two elements to look for when examining deductive arguments: valid logic and true premises. To say that a deductive argument is valid is to say that, due to the logical form, true premises will always lead to a true conclusion. The most basic argument form is the syllogism, and the most basic valid form of the syllogism is Modus Ponens. The logical form of the following arguments is Modus Ponens; thus, they are logically valid:
Argument A—false gods and false prophets
A1. If a person speaks in the names of false gods, that person is a false prophet.
A2. Muhammad spoke in the names of false gods.
A3. Therefore, Muhammad was a false prophet.
Argument B—false revelations and false prophets
B1. If a person delivers a revelation that doesn’t come from God, that person is a false prophet.
B2. Muhammad delivered a revelation that didn’t come from God.
B3. Therefore, Muhammad was a false prophet.
Since the logic of both arguments is valid, true premises will always lead to a true conclusion. Hence, if the premises of these arguments are true, Muhammad was a false prophet. Let us turn, then, to a careful discussion of our premises.
II. PREMISES A1 AND B1 DEFENDED
A1 and B1 seem intuitively obvious. That is, it seems clear that if a person speaks in the names of false gods or delivers revelations that don’t come from God, the person cannot be a true prophet. Nevertheless, by appealing to the Bible to bolster their belief in Muhammad, Muslims have inadvertently granted that A1 and B1 are true.
Deuteronomy 18 serves as the foundation of Islam’s "Argument from Biblical Prophecy," used by generations of Muslims to prove that Muhammad was a true prophet. Indeed, the popular Brief Illustrated Guide to Understanding Islam uses Deuteronomy 18 as its primary evidence that the Bible speaks of Muhammad. Author I. A. Ibrahim says,
The Biblical prophecies on the advent of the Prophet Muhammad are evidence of the truth of Islam for people who believe in the Bible.
In Deuteronomy 18, Moses stated that God told him: " I will raise up for them a prophet like you from among their brothers; I will put my words in his mouth, and he will tell them everything I command him. If anyone does not listen to my words that the prophet speaks in my name, I myself will call him to account." (Deuteronomy 18: 18-19) 
The book goes on to argue that Muhammad fulfilled this prophecy in numerous ways. While such claims have been refuted ad nauseum,  wwill simply note that Muslims have here granted that Deuteronomy 18:18-19 is inspired by God (since they regard it as a miraculous prophecy). Surely, then, we can’t ignore the next verse, where God says:
"But the prophet who speaks a word presumptuously in My name which I have not commanded him to speak, or which he speaks in the name of other gods, that prophet shall die." (Deuteronomy 18:20)
Here we have two criteria for spotting a false prophet: (1) delivering a revelation which God has not "commanded him to speak," and (2) speaking "in the name of other gods." Since Muslims who appeal to so-called biblical prophecies of Muhammad have given this passage their stamp of approval, they cannot deny the truth of A1 and B1. To sum up, Muslims have appealed to a passage in Deuteronomy 18, and that passage entails premises A1 and B1. Thus, according to Muslim claims, the first premise of each of the Deuteronomy Deductions is true.
III. PREMISES A2 AND B2 DEFENDED
We have seen that, according to a passage regarded by many Muslims as divine revelation, a person who either delivers a message that does not come from God or speaks in the names of false gods must be a false prophet. But this means that Muhammad was a false prophet, since he did both when he delivered the infamous "Satanic Verses."
We learn about the Satanic Verses, not from Christian or Jewish sources, but from early Muslim writings. Accounts of the Satanic Verses are given in a number of early sources, including: (1) Ibn Ishaq, (2) Wakidi, (3) Ibn Sa’d, (4) al-Tabari, (5) Ibn Abi Hatim, (6) Ibn al-Mundhir, (7) Ibn Mardauyah, (8) Musa ibn 'Uqba, and (9) Abu Ma'shar.  According to the great Muslim scholar Ibn Hajar, three chains of transmission (isnad) in these accounts "satisfy the conditions requisite for an authentic report." Moreover, Sahih al-Bukhari, Islam’s most trusted source on the life of Muhammad, gives indirect confirmation of the event (Number 4862, quoted below). Beyond this, certain verses of the Qur’an (17:73-5 and 22:52-3) were revealed in response to Muhammad’s embarrassing lapse into polytheism.
We therefore have compelling historical evidence that the story is authentic. (For a thorough discussion of the evidence for the Satanic Verses, see " Muhammad and the Satanic Verses.")
In fact, the historical method virtually guarantees the legitimacy of the story. Historians examining the lives of leaders and religious figures employ what is known as the " Principle of Embarrassment," a principle which also carries much weight in legal investigations. Law professor Annette Gordon-Reed sums up the principle thus: "Declarations against interest are regarded as having a high degree of credibility because of the presumption that people do not make up lies in order to hurt themselves; they lie to help themselves."  Applying the Principle of Embarrassment to accounts of the Satanic Verses, we see immediately that Muslims would not have invented this story, since it calls Muhammad’s reliability into question. We also see that the story couldn’t have been invented by non-Muslims; for if non-Muslims had invented the story, Muslims would have exposed the story’s origin, instead of defending it in their earliest historical works.
The evidence for the general reliability of the Muslim accounts concerning the Satanic Verses is therefore too overwhelming to ignore. With this in mind, let us consider a condensed account of what happened, based on the History of al-Tabari.
According to al-Tabari,
When the Messenger of God saw how his tribe turned their backs on him and was grieved to see them shunning the message he had brought to them from God, he longed in his soul that something would come to him from God which would reconcile him with his tribe. With his love for his tribe and his eagerness for their welfare it would have delighted him if some of the difficulties which they made for him could have been smoothed out, and he debated within himself and fervently desired such an outcome. Then God revealed:
By the Star when it sets, your comrade does not err, nor is he deceived; nor does he speak out of (his own) desire . . .
and when he came to the words:
Have you thought upon al-Lat and al-‘Uzza and Manat, the third, the other?
Satan cast on his tongue, because of his inner debates and what he desired to bring to his people, the words:
These are the high-flying cranes; verily their intercession is accepted with approval. (Al-Tabari, p. 108)
The polytheists were delighted that Muhammad had at last approved of their gods. To return the kindness, they "prostrated themselves because of the reference to their gods which they had heard, so that there was no one in the mosque, believer or unbeliever, who did not prostrate himself" (p. 109).
Muhammad’s friendly relations with the polytheists were short-lived, however, for he soon learned that his verses praising pagan idols came not from God, but from Satan. Saddened to recognize his treachery against Allah, Muhammad lamented: "I have fabricated things against God and have imputed to Him words which He has not spoken" (p. 111). Yet "Gabriel" comforted Muhammad, informing him that all prophets fall for Satan’s tricks from time to time. This staggering and unbelievable claim even found its way into the Qur’an:
" And We did not send before you any apostle or prophet, but when he desired, the Shaitan made a suggestion respecting his desire; but Allah annuls that which the Shaitan casts, then does Allah establish His communications, and Allah is Knowing, Wise." (Surahh 22:52) 
According to the next verse, Allah allows his prophets to receive revelations from Satan in order to test hard-hearted people.
Whatever we think of the preposterous Qur’anic explanation of the Satanic Verses (and its defense of Muhammad), it is clear that the Prophet of Islam, on at least one occasion, delivered a message that did not come from God. It is also clear that Muhammad, on at least one occasion, spoke in the names of false gods.  Thus, we can establish from Muslim sources that A2 and B2 are almost certainly true.
IV. POSSIBLE REPLIES
Since we have good reasons to accept premises A1, A2, B1, and B2, we have good reasons to accept conclusions A3 and B3, both of which claim that Muhammad was a false prophet. Muslims, however, will not want to accept this conclusion. Let us briefly discuss their prospects for rejecting it.
Muslims could, of course, claim that Deuteronomy 18:20 is a false teaching, not actually revealed by God. But if they take this route, it would be absurd of them to turn around and declare that 18:18-19 is an inspired prophecy. While it is alarmingly common for Muslims to pick and choose which passages in the Bible are correct (i .e. everything that agrees with Islam is correct, but everything that disagrees with Islam was corrupted by evil Jews and Christians), no one is going to be convinced by the claim that one verse in Deuteronomy 18 proves the prophethood of Muhammad, while another verse in the same passage is corrupted because it proves that he was a false prophet.
Thus, Muslims who want to deny A1 and B1 must abandon their claim that Deuteronomy 18 predicts the coming of Muhammad. The problem with this approach is that the prophecy of a coming messenger like Moses is one of the last remaining verses that Muslims—in spite of the evidence—cling to in their hopes of vindicating Muhammad. But if the Bible contains no clear prophecies about Muhammad, then Muhammad was a false prophet, since he claimed (in the Qur’an no less!) that the Jewish and Christian scriptures contain prophecies of his coming. This means that Muslims are caught between the horns of a dilemma. If they cling to Deuteronomy 18, then Muhammad was a false prophet. If they abandon it, then they are on the verge of having no biblical prophecies of Muhammad, which would imply that Muhammad was a false prophet.
Muslims who give up their most prized prophecy still wouldn’t be out of the water, however. For even if they abandon Deuteronomy 18 and declare it to be utterly corrupted, this wouldn’t refute A1 and B1, since, as I have already noted, these premises are intuitively obvious. Muslims who want to deny A1 and B1 must therefore show that these premises are false by arguing that genuine prophets can indeed deliver false revelations and speak in the names of false gods. We would love to see Muslims attempt to defend such an untenable position!
It seems, then, that Muslims who want to continue believing in Muhammad must deny not A1 and B1, but A2 and B2. But this means that they must reject the overwhelming historical evidence for Muhammad’s temporary support of paganism. Muslims who take this approach must do seven things. First, they must provide some reasonable explanation as to the story’s origin (e.g. they must make a plausible case that the story was invented by pagans, Jews, or Christians). Second, they must explain why Muslims, who had every reason to reject such a story, passed it on as if it were true (instead of exposing it as a fabrication). Third, they must show that Ibn Ishaq, Wakidi, Ibn Sa’d, al-Tabari, Ibn Abi Hatim, Ibn al-Mundhir, Ibn Mardauyah, Musa ibn ‘Uqba, and Abu Ma’shar were sloppy historians (so amazingly sloppy that they included false stories about Muhammad that called his prophethood into question). Fourth, they must account for the various chains of authority to which the early Muslim biographers appealed in their efforts to demonstrate the story’s authenticity. Fifth, they must explain why al-Bukhari, Islam’s most trusted authority, confirms certain details of the story that only make sense if Muhammad really did deliver the Satanic Verses. According to Bukhari,
The Prophet performed a prostration when he finished reciting Suraht an-Najm [Surahh 53], and all the Muslims and Al-Mushrikun (polytheists, pagans, idolaters, and disbelievers in the Oneness of Allah and in His Messenger Muhammad) and jinn and human beings prostrated along with him. (4862) 
Though Bukhari understandably omits the embarrassing reason for the prostration of the pagans, he inadvertently confirms the account given by Ibn Ishaq and the others, who faithfully reported that the pagans bowed down because Muhammad spoke favorably of their gods. Sixth, Muslims must account for Surahh 22:52, which, again, declares that all God’s prophets received revelations from Satan—a verse so preposterous that it could only have been offered to the Muslim community as an absurd explanation for something like the Satanic Verses. Seventh, they must show non-Muslims why we should reject all the available evidence and believe that Muhammad was spiritually reliable, when, as all informed Muslims will admit, Muhammad was the victim of black magic (a spell cast by a Jewish magician) and, at one point, was convinced that he was demon-possessed. Put differently, if the Prophet of Islam could mistakenly believe that he was demon-possessed, and was susceptible to spiritual attacks (such as black magic), why shouldn’t we believe that he could fall prey to revelations from Satan? (For more on Muhammad’s spiritual difficulties, see "A Bewitched Prophet?")
While we have witnessed Muslim attempts to explain away the historical evidence for the Satanic Verses, we have never seen anything remotely resembling a convincing refutation of the evidence. For instance, in David Wood’ debate on the prophethood of Muhammad at U.C. Davis, his opponent Ali Ataie tried to respond to al-Bukhari’s indirect confirmation of the Satanic Verses by appealing to the miraculous power of the Qur’an. According to Ataie, the reason the pagans bowed down in honor of Surahh 53 (which, in its present form, ridicules polytheism) was that they were overwhelmed by its majesty. But surely such a response is based on fantasy rather than fact. Muslims have been reciting the Qur’an for more than a thousand years, and unbelievers are typically quite unimpressed by Muhammad’s poetry. Indeed, Muhammad won remarkably few converts when he appealed to the Qur’an as evidence of his divine commission. He only saw large numbers of converts when he turned to other (far more bloody) means of conversion. Thus, for Muslims like Ataie to claim that the pagans, with one accord, bowed down at Muhammad’s recitation of Surahh 53, is bordering on delusional. Bukhari’s hadith makes far more sense when read in the light of historical works like Ibn Ishaq (which, incidentally, predates Sahih al-Bukhari by many decades). The only conceivable reason the pagans would bow down in honor of Surahh 53 is that the Surahh originally supported paganism, and this is exactly what our earliest historical records claim.
All things considered, the only reasonable conclusion to be drawn from the historical evidence is that Muhammad, in a moment of weakness, gave into temptation and actively promoted polytheism by delivering a revelation from Satan. But this means that we cannot rationally reject premises A2 and B2. Muslims, then, can have no good response to the Deuteronomy Deductions. We are therefore left with an unavoidable conclusion: Muhammad was a false prophet.
To conclude, we would like to emphasize again that the entire argument (in two deductions) has been based on the writings and claims of Muslims. Early Muslim historians, in an astounding display of honesty and integrity, admitted that their prophet had delivered the Satanic Verses to his listeners. In acknowledging this, they provided all the evidence we need for premises A2 and B2. Modern Muslims, in an effort to defend Muhammad’s claim to biblical support for his ministry, have granted that a passage in Deuteronomy 18 was inspired by God. In doing so, they have given us all the evidence we need for premises A1 and B1. Since both of the Deuteronomy Deductions are logically valid, we have two proofs, based entirely on the claims of Muslims, that Muhammad was a false prophet.
Since the Deuteronomy Deductions are sound (i.e. logically valid with true premises), any honest seeker will have to admit that Muhammad was a false prophet. It should be an enlightening exercise, then, to present these arguments to Muslims. If a Muslim examines the arguments carefully, inspecting the premises and weighing the evidence, and then rejects the conclusion without refuting the argument, we can only assume that such a person is less interested in truth and more interested in the comfort provided by blindly accepting the faith he was raised in. Although experience leads to believe that most Muslims are of this type, personal experience has also shown that there are Muslims in the world who are actively dedicated to learning the truth about God. The first truth such Muslims must learn is that their prophet Muhammad was no prophet at all. The second is that their prophet Jesus is much more than a prophet.
1 Bible quotations are from the New American Standard Bible, Updated Edition.
2 The History of al-Tabari, Volume VI: Muhammad at Mecca, W. Montgomery Watt and M. V. McDonald, trs. (Albany: State University of New York Press, 1988).
3 Modus Ponens takes the form:
1. If P, then Q.
3. Therefore, Q.
Here we may substitute various elements for P and Q, giving us, for instance:
1. If Fido is a dog, then Fido is a mammal.
2. Fido is a dog.
3. Therefore, Fido is a mammal.
4 Ibrahim, I. A. A Brief Illustrated Guide to Understanding Islam (Houston: Darussalam, 1997), p. 33.
5 See, for example, "Muhammad in the Bible?"
6 For references, see "Muhammad and the Satanic Verses."
7 Ibn Hajar, quoted in Allam Shibli Nu’mani, Siraht-un-Nabi, Volume
8 Annette Gordon-Reed, Thomas Jefferson and Sally Hemings: An American Controversy (Charlottesville: University of Virginia Press, 1997).
9 Qur’an quotations are from the M. H. Shakir translation.
10 One might object that Muhammad did not actually speak in the names of the pagan gods. That is, he did not say, "I come to you in the name of Manat." Instead, he spoke in the name of Allah, and merely approved of the intercession of the pagan gods. However, the point of the passage in Deuteronomy is clearly that anyone who promotes polytheism is a false prophet. And Muhammad certainly promoted polytheism on this occasion.
11 Sahih Al-Bukhari, Volume Six, Muhammad Muhsin Khan, tr. (Riyadh: Darussalam, 1997).