 The latter had the backing of the Banu Tamim, a powerful tribal faction in the Khurasan army, while al-Muhallab lacked tribal support as the Azd presence in the province was negligible at the time.Iraq, and Khurasan with it, ultimately came under the suzerainty of the anti-Umayyad, Mecca-based caliph, Abd Allah ibn al-Zubayr (), who appointed al-Muhallab governor of Khurasan.Meanwhile, a mass wave of Azdi tribesmen from Oman had migrated to Basra between 679 and 680, merged with the Azd Sarat already present in the city and formed a strong alliance with the Rabi'a tribal confederation, a major faction in the Basran garrison.