72 of his family members and followers were killed in the Battle of Karbala. Shīʿa Muslims regard Ḥusayn ibn ʿAlī as a martyr (shahid), and count him as an Imam from the Ahl al-Bayt. They view Ḥusayn ibn ʿAlī as the defender of Islam from annihilation at the hands of Yazid I. Ḥusayn is the last Imam following ʿAlī mutually recognized by all branches of Shīʿa Islam. The Battle of Karbala and martyrdom of Ḥusayn ibn ʿAlī is often cited as the definitive separation between the Shīʿa and Sunnī sects of Islam, and is commemorated each year by Shīʿa Muslims on the Day of Ashura. Imamate of the Ahl al-Bayt Later, most denominations of Shīʿa Islam, including Twelvers and Ismāʿīlīs, became Imamis. Imami Shīʿītes believe that Imams are the spiritual and political successors to Muhammad. Imams are human individuals who not only rule over the Muslim community with justice, but also are able to keep and interpret the divine law and its esoteric meaning. The words and deeds of Muhammad and the Imams are a guide and model for the community to follow; as a result, they must be free from error and sin, and must be chosen by divine decree (nass) through Muhammad. According to this view peculiar to Shīʿa Islam, there is always an Imam of the Age, who is the divinely appointed authority on all matters of faith and law in the Muslim community. ʿAlī was the first Imam of this line, the rightful successor to Muhammad, followed by male descendants of Muhammad through his daughter Fatimah. This difference between following either the Ahl al-Bayt (Muhammad's family and descendants) or pledging allegiance to Abū Bakr has shaped the Shīʿa—Sunnī divide on the interpretation of some Quranic verses, ḥadīth literature (accounts of the sayings and living habits attributed to the Islamic prophet Muhammad during his lifetime), and other areas of Islamic belief throughout the history of Islam. For instance, the ḥadīth collections venerated by Shīʿa Muslims are centered on narrations by members of the Ahl al-Bayt and their supporters, while some ḥadīth transmitted by narrators not belonging to or supporting the Ahl al-Bayt are not included. Those of Abu Hurairah, for example, Ibn Asakir in his Taʿrikh Kabir, and Muttaqi in his Kanzuʿl-Umma report that ʿUmar ibn al-Khaṭṭāb lashed him, rebuked him, and forbade him to narrate ḥadīth from Muhammad. ʿUmar is reported to have said: "Because you