From the eighth century onwards, Christians living under Islam have produced numerous apologetic and polemical works, aimed at proving the continuing validity of Christianity. Among these is the Legend of Sergius Baḥīrā, which survives in two Syriac and two Arabic versions, and appears here in edition and translation. Being a counterhistory of Islam, it reshapes early Muslim traditions about a monk recognizing Muḥammad as the final Prophet by turning this monk into Muhammad’s tutor and co-author of the Qur’an. In response to Muslim triumphalist propaganda, it portrays Islam’s political power as predestined but finite and unrelated to its religious message. This feature sets the legend apart from similar Christian accounts of the origin of Islam, East and West, which are reviewed in this study as well.