Criticism of Muhammad has existed since the 7th century AD, when Muhammad was decried by his non-Muslim Arab contemporaries for preaching monotheism, and by 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 (מְשֻׁגָּע, "the Madman" or "the Possessed"). During the Middle Ages, various Western and Byzantine Christian thinkers considered Muhammad to be a perverted, deplorable man, a false prophet, and even the Antichrist, as he was frequently seen in Christendom as a heretic or possessed by demons. Some of them, like Thomas Aquinas, criticized Muhammad's handling of doctrinal matters and his promises of carnal pleasure in the afterlife. Modern criticism has concerned Muhammad's sincerity as a prophet, his morality, his marriages, his ownership of slaves and his psychological condition. Muhammad has also been accused of sadism and cruelty in the treatment of his enemies, including in the invasion of the Banu Qurayza tribe in Medina. Criticism of IslamList of critics of IslamChristianity and Islam and Muhammad's views on Christians Medieval Christian views on Muhammad 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". Another Greek source for Muhammad is Theophanes the Confessor, a 9th-century writer. The earliest Syriac source is the 7th-century writer John bar Penkaye.