The Muslims were assisted by some Copts, who found the Muslims more tolerant than the Byzantines, and of these some turned to Islam. In return for a tribute of money and food for the occupation troops, the Christian inhabitants of Egypt were excused from military service and left free in the observance of their religion and the administration of their affairs. Others sided with the Byzantines, hoping that they would provide a defense against the Arab invaders. During the reign of Caliph Ali, Egypt was captured by rebel troops under the command of former Rashidun army general Amr ibn al-As, who killed Muhammad ibn Abi Bakr, the governor of Egypt appointed by Ali.