 In 690, eight months after he was reassigned to the war against the Azariqa, Mus'ab was defeated and killed by the Umayyad army led by Caliph Abd al-Malik ibn Marwan at the Battle of Maskin.At the time, al-Muhallab was engaged against the Azariqa in the environs of Ahwaz.Upon hearing news of Abd al-Malik's victory and conquest of Iraq, al-Muhallab had his troops swear allegiance to the Umayyad caliph.