According to the treaty of Ahwaz, while some parts of the province of Khuzistan were under the direct rule of the Muslims, Ahwaz proper and the rest of the province were ruled by Hormuzan as a vassal of the Muslims.
Restored to power, Hormuzan tried to build up a force in a bid to have another contest with the Muslims. He recruited a large number of Kurds from his ancestral district of Mihirjanqazuf. He even incited the Persians in the Muslim zone to join him so that another effort might be made to overthrow the Muslims.
The Muslim commander Salma reported of these developments to Abu Musa the Governor of Basra who had taken over after the death of Utba. Abu Musa in turn asked for the instructions of Hazrat Umar. The Caliph ordered that the Muslims should capture Ahwaz.
Abu Musa the Governor of Basra marched with the Muslim forces to Ahwaz. For some time the two opposing forces lay encamped on either side of the Karun, and there was the usual exchange of emissaries. The negotiations broke down, and it was decided that an engagement should be risked.
Hormuzan gave the Muslims the option to cross the Karun and come over to the side of the Persians, or let the Persians cross and come over to the side of the Muslims. Heretofore the Muslims generally refrained from crossing the river, and generally asked the Persians to cross over to their side. That was the stage when by way of abundant caution the Muslims wanted to remain as close to the desert as possible. Now things had changed, and the Muslims had advanced too far inland, and the question of proximity to the desert no longer arose. Abu Musa accordingly decicied that the Muslims would cross over to the Persian side of the river. After crossing the river, Abu Musa took special steps to ensure that the bridge by which they had crossed remained heavily guarded.
After the Muslims had crossed, the forces of the two sides were deployed for action. For some time the contest was fierce, and there were casualties on both sides. The Muslims increased their pressure, and the Persians could not hold the ground. They began to fall back and Hormuzan found safety in flight. Hormuzan with his force withdrew to Ram Hormuz.
After the withdrawal of the Persian forces, Ahwaz was occupied by the Muslims. Abu Musa sent a pursuit column under Juzz b. Muawia to follow the retreating Persians. The Muslims caught up with the retreating Persians, but Hormuzan resorted to rearguard action avoiding a decisive engagement.
The Muslims occupied Dauraq the chief city of the district of Surraq. Hormuzan retired east of the river at Arbuk and here he took a stand. The Muslims prepared for battle, but Hormuzan sent an emissary and sued for peace. Juzz reported the developments to Abu Musa and Abu Musa in turn referred the matter to Umar.
Umar gave orders that the offer of peace be accepted. According to the peace terms the districts of Ahwaz and Dauraq were annexed by the Muslims. The rest of the princedom of Hormuzan was left to him and he shifted his capital from Ahwaz to Ram Hormuz. Hormuzan cleared the arrears of Jizya and undertook to pay Jizya regularly in future. At Ahwaz and Dauraq a considerable booty fell to the share of the Muslims. After distributing four-fifth, the rest of the booty was sent to Umar as the state share.