This important work is a source-critical study of a group of traditions (ahadith) found in Ibn Ishaq's Biography (Sira) of the prophet Muhammad, widely considered one of the most important early historical texts on the Prophet's life. Through a meticulous isnad-cum-matn analysis, the author reveals that Ibn Ishaq relied on Muhammad b. Abi Muhammad, a hitherto undocumented source of his. Important new light is also shed on problems with Ibn Hisham's recension of Ibn Ishaq's Sira.