Criticism of Muhammad

The first to criticize the Islamic prophet Muhammad were his non-Muslim Arab contemporaries, who decried him for preaching monotheism, and the Jewish tribes of Arabia, for what they claimed were unwarranted appropriation of Biblical narratives and figures and vituperation of the Jewish faith. For these reasons, medieval Jewish writers commonly referred to him by the derogatory nickname ha-Meshuggah (Hebrew: מְשֻׁגָּע‬, "the Madman" or "the Possessed").

During the Middle Ages, various Western and Byzantine Christian polemicists considered Muhammad to be a deplorable man, a false prophet, and even the Antichrist, as he was frequently seen in Christendom as a heretic or possessed by demons. Thomas Aquinas criticized Muhammad's handling of doctrinal matters and promises of what Aquinas described as "carnal pleasure" in the afterlife.

Modern criticism, primarily from non-Muslim and predominantly Western authors, has raised questions about Muhammad’s prophetic claims, personal conduct, marriages, slave ownership, and mental state. Criticism has also focused on his treatment of enemies, particularly in the case of the Banu Qurayza tribe in Medina. Muslim scholars often respond by emphasizing the historical context of 7th-century Arabia and Muhammad’s role in promoting justice and social reform. Some historians say the punishment of the Banu Qurayza reflected the norms of the time and was ordered by Sa'd ibn Mu'adh, though others question Muhammad’s role or the scale of the event.

According to sociologist Rodney Stark, "the fundamental problem facing Muslim theologians vis-à-vis the morality of slavery" is that Muhammad himself engaged in activities such as purchasing, selling, and owning slaves, and that his followers saw him as the perfect example to emulate. Stark contrasts Islam with Christianity, writing that Christian theologians wouldn't have been able to "work their way around the biblical acceptance of slavery" if Jesus had owned slaves, as Muhammad did.

Forough Jahanbaksh notes that Muhammad never preached the abolition of slavery as a doctrine, although he did moderate the age-old institution of slavery, which was also accepted and endorsed by the other monotheistic religions, Christianity and Judaism, and was a well-established custom of the pre-Islamic world. According to Murray Gordon, Muhammad saw it "as part of the natural order of things". While Muhammad did improve the condition of slaves, and exhorted his followers to treat them with kindness and compassion, and encouraged freeing of slaves, he still did not completely abolish the practice.

His decrees greatly limited those who could be enslaved and under what circumstances (including barring Muslims from enslaving other Muslims), allowed slaves to achieve their freedom and made freeing slaves a virtuous act. Some slaves earned respectable incomes and achieved considerable power, although elite slaves still remained in the power of their owners. Muhammad established a system to encourage manumission, and several of his companions, including Abu Bakr and Uthman ibn Affan, are recorded to have freed thousands of slaves, often purchasing them for this purpose. Many early converts to Islam were the poor and former slaves like Bilal ibn Rabah al-Habashi.

Norman Geisler accuses Muhammad of "mercilessness" towards the Jewish tribes of Medina. Geisler also argues that Muhammad "had no aversion to politically expedient assassinations", "was not indisposed to breaking promises when he found it advantageous" and "engaged in retaliation towards those who mocked him." The Orientalist William Muir, in assessing Muhammad's character, described him as cruel and faithless in dealing with his enemies.

Jean de Sismondi suggests that Muhammad's successive attacks on powerful Jewish colonies located near Medina in Arabia were due to religious differences between them, and he claimed that he subjected the defeated to punishments that were not typical in other wars.