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Jewish criticism Main article: Judaism's views on Muhammad In the Middle Ages, it was common for Jewish writers to describe Muhammad as ha-meshuggah ("The Madman"), a term of contempt frequently used in the Bible for those who believe themselves to be prophets.

Christian criticism Early middle ages The earliest (documented) Christian knowledge of Muhammad stems from Byzantine sources, written shortly after Muhammad's death in 632. In the Doctrina Jacobi nuper baptizati, a dialogue between a recent
Christian convert and several Jews, one participant writes that his brother "wrote to [him] saying that a deceiving prophet has appeared amidst the Saracens". Another participant in the Doctrina replies about Muhammad:

"He is deceiving. For do prophets come with sword and chariot?, …[Y]ou will discover nothing true from the said prophet except human bloodshed".
 One Christian who came under the early dominion of the Islamic Caliphate was John of Damascus (c. 676–749 AD), who was familiar with Islam and Arabic. The second chapter of his book, The Fount of Wisdom, titled "Concerning Heresies", presents a series of discussions between Christians and Muslims.

 John claimed an Arian monk (whom he did not know was Bahira) influenced Muhammad and viewed the Islamic doctrines as nothing more than a hodgepodge culled from the Bible. From the 9th century onwards, highly negative biographies of Muhammad were written in Latin, such as the one by Alvarus of Cordoba proclaiming him the Anti-Christ.