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However many early history books like the Islamic Conquest of Syria Fatuhusham by al-Imam al-Waqidi state that after the conversion to Islam Muawiyah's father Abu Sufyan ibn Harb and his brothers Yazid ibn Abi Sufyan were appointed as commanders in the Muslim armies by Muhammad. Muawiyah, Abu Sufyan ibn Harb, Yazid ibn Abi Sufyan and Hind bint Utbah fought in the Battle of Yarmouk. The defeat of the Byzantine Emperor Heraclius at the Battle of Yarmouk opened the way for the Muslim expansion into Jerusalem and Syria.

Who was the Byzantine leader at the Battle of Yarmouk?
Heraclius