As soon as the news of Hasan's selection reached Mu'awiya, who had been fighting Ali for the caliphate, he condemned the selection, and declared his decision not to recognize him. Letters exchanged between them before their troops faced each other were to no avail. Hasan sent his vanguard of twelve thousand men to move to Maskin, under Ubayd Allah ibn al-Abbas. There, he was told to hold Mu'awiya's army, until Hasan arrived with the main army. Hasan, however, was facing a problem at Sabat near al-Mada'in, where he gave a sermon. Taking this as a sign that Hasan was preparing to give up battle and make peace with Mu'awiya, some of his troops rebelled against him. Hasan rode off surrounded by his partisans, but was wounded by a Kharijite. The news of the attack, having been spread by Mu'awiya, further demoralized the already discouraged army of Hasan. Ubayd Allah, accepted Mu'awiya's bribe and deserted. According to Veccia Vaglieri, 8000 men out of 12000 followed the example of their general. Mu'awiya, who had already started negotiations with Hasan, now sent high-level envoys, while committing himself in a witnessed letter to appoint Hasan his successor, along with some other conditions, provided Hasan surrender the reign to him. Thus Hasan abdicated to Mu'awiya, the founder of the Umayyad dynasty to end the First Fitna. For the rest of his life, Hasan retired in Medina, trying to keep aloof from political involvement for or against Mu'awiya, until he died. His wife, Ja'da bint al-Ash'at, is commonly accused of having poisoned him at the instigation of Mu'awiya.