Christian and Muslim accounts of pre-Islamic religion shared a single source tradition

Evidence

John of Damascus’ account of the jahiliyyah is almost identical to that of Ibn al-Kalbi, who derived his information from his father, Muhammad b. Al-Said al-Kalbi (d. 763), a contemporary to John of Damascus. Both present jahiliyyah as the Abrahamic tradition which, however, deteriorated into a crude polytheism and litholatry” (Sahas, “Arab Character,” 197-98). — John V. Tolan, Saracens, 1525

Categorization

• XREF: Confirms that early Christian polemicists and Muslim historians drew on the same collective memory of jahiliyyah — complicates any simple oppositional-genealogy reading of Christian anti-Islam sources.
• QUESTION: If John of Damascus’ account mirrors Ibn al-Kalbi exactly, how much of what Christian polemics ‘invented’ about Islam was actually recycled Muslim self-description?