He therefore took up residence at al-Madīnah al-Hāshimiyyah, installing himself in the Palace of the Governorship. By then he had grown cold toward Abū Salamah al-Khallāl, for it had reached him that Abū Salamah wished to divert the caliphate from the descendants of al-ʿAbbās to the family of ʿAlī ibn Abī Ṭālib. Allah, glorified and exalted is He, knows best.

Account of the slaying of Marwān ibn Muḥammad ibn Marwān, the last of the Umayyad caliphs, and the transfer of the caliphate to the Banū al-ʿAbbās

This occurred in fulfilment of His words: “Allah bestows His sovereignty upon whom He wills” (Q. 2:247) and His saying: “Say, ‘O Allah, Master of sovereignty…’” (Q. 3:26).

We have already related that when Marwān learned of Abū Muslim, his followers, and the events that had unfolded in Khurāsān, he left Ḥarrān and camped on the river called the Zab, near Mosul, in the region of al-Jazīrah. News then reached him that al-Saffāḥ had been given the pledge of allegiance in Kufah, that the troops had rallied to him, and that his authority was now secure. This weighed upon Marwān greatly, so he mustered his forces. Against him advanced Abū ʿAwn ibn Abī Yazīd—one of al-Saffāḥ’s commanders—with a large army; they confronted each other at the Zab, and reinforcements continued to reach Abū ʿAwn from al-Saffāḥ.

Al-Saffāḥ next summoned the members of his household who were apt for combat, urging them to go forth. ʿAbdallāh ibn ʿAlī volunteered, saying, “Proceed, with the blessing of Allah.” He set out with many contingents and arrived at Abū ʿAwn’s camp, whereupon Abū ʿAwn vacated his own pavilion for him and left all that it contained at his disposal. ʿAbdallāh ibn ʿAlī placed Ḥayyāsh ibn Ḥabīb al-Ṭāʾī and Naṣīr ibn al-Muḥtafiz in charge of his security force. Meanwhile Abū al-ʿAbbās sent Mūsā ibn Kaʿb with thirty men by the courier service to ʿAbdallāh ibn ʿAlī, urging him to take the initiative against Marwān, to hasten to engage him, and to fight him before circumstances could change and the fires of war cool.

ʿAbdallāh ibn ʿAlī advanced with his troops until he faced Marwān’s army. Marwān, too, rose with his soldiers, and at first light the two forces drew up in battle array.

It is said that Marwān had with him that day one hundred and fifty thousand men; others say one hundred and twenty thousand. ʿAbdallāh ibn ʿAlī had twenty thousand.

Marwān said to ʿAbd al-ʿAzīz ibn ʿUmar ibn ʿAbd al-ʿAzīz, “If the sun passes its zenith today and they have not fought us, then we shall be the ones to hand it over to Jesus son of Mary; but if they fight us before noon, then we belong to Allah and to Him we return.”

Marwān then sent to ʿAbdallāh ibn ʿAlī asking for a truce. ʿAbdallāh replied, “Ibn Zurayq lies! The sun will not pass its zenith before I have the horses trample him, Allah willing.” This was on a Saturday, eleven nights having passed of Jumādā al-Ākhirah of that year.

Marwān said to the people of Syria, “Stand fast; do not initiate the fighting,” and he kept his gaze fixed on the sun. Al-Walīd ibn Muʿāwiyah ibn Marwān—his son-in-law, married to his daughter—defied him and charged. Marwān grew angry and reviled him. The men on the Syrian right wing attacked, whereupon Abū ʿAwn withdrew to ʿAbdallāh ibn ʿAlī. Mūsā ibn Kaʿb fought on ʿAbdallāh’s side.

ʿAbdallāh ordered the troops to dismount, and the cry was raised: “To the ground! To the ground!” They dismounted, planted their lances, knelt upon their knees, and fought. The Syrians began to fall back as though being driven. Advancing on foot, ʿAbdallāh kept saying, “Lord, how long shall we be slain for Your sake?” He shouted, “People of Khurāsān! Vengeance for Ibrāhīm the Imām! O Muḥammad! O Manṣūr!” The fighting then grew exceedingly fierce between the two sides.