Medieval Christian polemic traced Muhammad’s error to heretical Jewish and Christian teachers

Evidence

Both Alfonsi and the Liber denudationis portray Islamic ritual and belief as a confused hodgepodge of heretical Christianity, heretical Judaism, and idolatrous survivals. Both stress the role of Muhammad’s heretical teachers. For the Liber denudationis, they are the monk “Boheira” (i.e., Bahira), the Jew ‘Abd Allâh ibn Salâm, and the Persian Salmân al-Fârisî; for Alfonsi, Muhammad was educated by a Jacobite heretic named Sergius (who, he says, had been condemned by a council of Antioch) and by two Jewish heretics, Abdias (perhaps ‘Abd Allâh b. Salâm) and Ka’b al-Ahbâr. For this reason, both authors suggest, Muslim doctrine contains a mixture of truth and error, its ritual a blend of Jewish practice and paganism. — John V. Tolan, Saracens, 811

Categorization

• XREF: Central genealogical root: the medieval template of Islam as derivative heresy (from Bahira/Sergius the heretical monk legend) is the ancestor of claims the vault already holds about Islam being framed as a corrupted offshoot.
• QUESTION: Worth chasing: how does the Bahira/Sergius legend lineage persist or mutate in later polemics up to the early modern period?