Complex sentence: Qaqa defeated the Persian army at Husaid, the remaining army retreated to Khanafis, where when the commander of the army at Khanafis heard about the Muslim's victory at Husaid withdraw his forces to Muzayyah and joined the Christian Arabs.
Split into simpler sentences: Qaqa defeated the Persian army at Husaid, and the remaining army retreated to Khanafis. Thus the commander of the army at Khanafis heard about the Muslim's victory at Husaid; he withdraw his forces to Muzayyah and joined the Christian Arabs.