Islam was framed by Byzantine chroniclers as an offshoot Christian-Jewish heresy

Evidence

Theophanes, fully aware of the religious motivations behind the Muslim conquests, characterizes Islam as a heresy composed of a mixture of Jewish and Christian elements; he later refers to Mecca as “the place of their blasphemy.” He is less clear about why God allowed these Muslim heretics to conquer vast territories. At times he blames the corruption and ineptitude of Byzantine officials, such as the eunuch who refuses to pay Arab mercenaries who had been defending Roman Syria from the Muslims; the mercenaries quickly switch sides and act as scouts for the invading Muslims. — John V. Tolan, Saracens, 410

Categorization

• XREF: This is a direct genealogical root for the tropes of Islam-as-heretical-deviation and ‘place of blasphemy’ that echo in vault claims about how the West constructed Islam as a distorted derivative of Judeo-Christian revelation. — connects to: Orthodox Islam and Christianity hold mutual heresy accusations rooted in Crusade history — Aijaz Ahmad, In Theory: Classes, Nations, Literatures, 784