The Muslim invasion of Fars began in 638/9, when the Rashidun governor of Bahrain, al-'Ala' ibn al-Hadrami, having defeated some rebellious Arab tribes, seized an island in the Persian Gulf. Although al-'Ala' and the rest of the Arabs had been ordered to not invade Fars or its surrounding islands, he and his men continued their raids into the province. Al-'Ala quickly prepared an army which he divided into three groups, one under al-Jarud ibn Mu'alla, the second under al-Sawwar ibn Hammam, and the third under Khulayd ibn al-Mundhir ibn Sawa.

When the first group entered Fars, it was quickly defeated and al-Jarud was killed. The same thing soon happened to the second group. However, the third group was more fortunate: Khulayd managed to keep the defenders at bay, but was unable to withdraw to Bahrain, as the Sassanians were blocking his way to the sea. Umar, having found out about al-'Ala's invasion of Fars, had him replaced with Sa'd ibn Abi Waqqas as governor. Umar then ordered Utbah ibn Ghazwan to send reinforcements to Khulayd. Once the reinforcements arrived, Khulayd and some of his men managed to withdraw to Bahrain, while the rest withdrew to Basra.