The Expedition of Usama bin Zayd was a military expedition of the early Muslim Caliphate led by Usama ibn Zayd that took place in June 632, in which Muslim forces raided Byzantine Syria. The expedition came three years after the Battle of Mu'tah. After the Farewell Pilgrimage, the Islamic 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. Muhammad sent Usama to Syria to avenge the Muslims' defeat at the Battle of Mu'tah, in which Usama's father and Muhammad's adopted son, Zayd ibn Harithah, had been killed. Usama's campaign was successful and his army was the first Muslim force to successfully invade and raid Byzantine territory, thus paving the way for the subsequent Muslim conquest of the Levant and Muslim conquest of Egypt, both of which took place during Usama's lifetime. Background 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 Muhammad and the forces of the Byzantine Empire and their Arab Christian Ghassanid 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 (including Usama's father, Zayd ibn Harithah), 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, 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. 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, the campaign was delayed and Abu Bakr was elected as Caliph in Medina. With the death of Muhammad,