Most of Islamic history was transmitted orally until after the rise of the Abbasid Caliphate. Historical works of later Muslim writers include the traditional biographies of Muhammad and quotations attributed to him—the "sira" and "hadith" literature—which provide further information on Muhammad's life. The earliest surviving written "sira" (biography of Muhammad) is "Sirat Rasul Allah" ("Life of God's Messenger") by Ibn Ishaq (d. 761 or 767 CE). Although the original work is lost, portions of it survive in the recensions of Ibn Hisham (d. 833) and Al-Tabari (d. 923). Many scholars accept these biographies although their accuracy is uncertain. Studies by J. Schacht and Ignác Goldziher have led scholars to distinguish between legal and historical traditions. According to William Montgomery Watt, although legal traditions could have been invented, historical material may have been primarily subject to "tendential shaping" rather than being invented. Modern Western scholars approach the classic Islamic histories with circumspection and are less likely than Sunni Islamic scholars to trust the work of the Abbasid historians.