During Ali 's Caliphate , the Muslim world became divided and rebellion broke out against the ruling Ali by Muawiyah I . When Ali was assassinated by Ibn Muljam , ( a Kharijite ) in 661 , his eldest son Hasan succeeded him but soon signed a peace treaty with Muawiyah to avoid further bloodshed . In the treaty , Hasan was to hand over power to Muawiya on the condition that he be just to the people and keep them safe and secure and that he would not establish a dynasty . After the death of Hasan in 670 , his younger brother Husyan became the head of Banu Hashim . His father 's supporters in Kufah gave him their allegiance . However , he told them he was still bound by the peace treaty between Hasan and Muawiyah as long as the latter was alive
Ali was assassinated
Assassination of Ali
Battle of Karbala