The Battle of Mu'tah was fought in September 629 near the village of Mu'tah, east of the Jordan River and Karak, between the forces of the Islamic prophet Muhammad and of the Byzantine Empire and their Arab ChristianGhassanid vassals. In Islamic historical sources, the battle is usually described as the Muslims' attempt to take retribution against the Ghassanids after a Ghassanid official executed Muhammad's emissary who was en route to Bosra. During the battle the Muslim army was routed. After three Muslim leaders, were killed, the command was given to Khalid ibn al-Walid and he succeeded in saving the rest of the forces. The surviving Muslim forces retreated to Medina. After the Farewell Pilgrimage in 632, the Prophet Muhammad appointed Usama ibn Zayd as the commander of an expeditionary force which was to invade the region of Balqa in the Byzantine Empire. The stated aim of this expedition was to avenge the Muslim losses at the Battle of Mu'tah, in which Usama's father and Muhammad's adopted son, Zayd ibn Harithah, had been killed.
Invasion
Usama was ordered by Muhammad to attack Balqa and Darum. Some weeks later, Muhammad fell ill, and Muslim elders such as Abu Bakr and Umar resisted going under the command of Usama because they thought that he, who was 20 at the time, was too young to lead an army. Muhammad dismissed these concerns. This incident is also mentioned in the Sahih al-Bukhari, which states that: It is also mentioned in and. Usama gathered a force of approximately 3000 men, of which 1000 were cavalry soldiers, and Abu Bakr had intended on joining Usama on campaign. Usama had also sent spies ahead of him, from which he learned that the enemy were still unaware of the imminent approach of his army. However, due to Muhammad's death on 8 June 632, the campaign was delayed and Abu Bakr was elected as Caliph in Medina. With the death of Muhammad, certain companions of the Prophet tried to persuade Abu Bakr, who succeeded Muhammad as leader of the Islamic community, to replace Usama as commander of the army with Umar Ibn Al-Khattab, due to Usama's youth. However, Abu Bakr reaffirmed the decision of Muhammad and dispatched the expedition under Usama's leadership. He then requested that Usama allow Umar ibn al-Khattab to stay behind in Medina to help in the administration, and Usama obliged. According to Al-Tabari, before Usama headed out and raided the inhabitants of Syria, Abu Bakr commanded Usama to follow ten rules of war. The tradition of the ten rules of Abu Bakr is also mentioned in the SunniHadith collection of Al-Muwatta.: Al-Tabari states that the expedition was successful and Usama: This success demonstrated the strength and cohesiveness of the Muslims and the Rashidun Caliphate even in the absence of Muhammad, because of his teachings. The army of Usama reached Syria and became the first Muslim force to successfully raid Byzantine territory, thus paving the way for the subsequent Muslim conquests of Syria and Egypt from the Byzantine Empire.