Hasan ibn Ali was an Alid political and religious leader. He was the eldest son of Ali and Fatima, and the eldest grandson of the Islamic prophet Muhammad. He briefly ruled as caliph from January to August 661 and is regarded as the second Imam in Shia Islam, succeeding his father, Ali, and preceding his younger brother, Husayn. Hasan is a member of the Ahl al-Bayt and the Ahl al-Kisa, and participated in the Event of the Mubahala. Muhammad described Hasan and Husayn as the leaders of the youth of paradise.