Christian writers called Muslims ‘new Jews’ from the eighth century on

Evidence

The Christian imagination proved more than willing to provide the help needed. … Agobard (ca. 779-840), for example, would confirm that Muslims, too, are descendants of Abraham. From the eighth century on, Christian writers would begin to refer to Muslims as being “new Jews” or “consistently characterize Islamic belief and practice as Jewish, or at least as Jewishly influenced.” — Gil Anidjar, The Jew, the Arab, 214

Categorization

• XREF: ‘New Jews’ is the exact phrase later scholarship uses about antisemitism-Islamophobia continuity; this grounds the genealogy in 8th-9th c. sources.
• SHARE: The Galatians 4 allegory mapping Hagar to both Mount Sinai-in-Arabia and present Jerusalem is the scriptural hinge Christian writers used to tie Jews and Muslims to Abraham.