Hasan–Muawiya treaty

In 661 CE, after Ali's death, Hasan ibn Ali attained to the caliphate. There was a military conflict between Hasan and Muawiya; and to avoid the agonies of another civil war, Hasan signed the Hasan–Muawiya treaty with Muawiyah, according to which Muawiyah wouldn't name a successor during his reign and let the Islamic world choose their successor after the latter.