Ibn Ishaq is generally regarded to be the earliest author of the Prophet Mohammed's biography (sira). Ibn Ishaq was able to make the most of Medinan authors who preceded him, including luminaries such as Asim ibn Omar, Yazid ibn Ruman and Ibn Shihab Al Zuhri as well as Urwah ibn Alzubair, Aban bin Othman and Musa ibn Uqba. Additionally, Ibn Ishaq's Sira relied on such sources as the Israeliyat—Arabic sources on the lives of the prophets, based on the Old and New Testaments—and contemporaneous oral histories of the prophet. Ibn Ishaq's achievement was that he introduced a completely new form of Arabic literature, totally separate to the Hadith, or Koranic exegesis (Tafsir), the two sources on which Sira relied. The emergence of this new genre can be understood as a response to the need of Muslim society to immortalize the memory of the Prophet and make him an example to be emulated, but without the total renouncement of the pre-Islamic heritage, in which stories were a prime and influential element. In its method and structure, the sira of Ibn Ishaq is considered the nucleus for the development of many other Islamic disciplines such as history and short biography (tabaqat), which included, alongside histories of the prophets, the nations, and the Muslims, and the biographies of the sahaba and the tab'iun, a section devoted to the sira.