Occupation of Uballa. After winning the battle of Kazima, Khalid rested his men for a few days and then advanced further inland in Iraq. Khalid sent a contingent under Ma'qal bin Muqarrin to occupy Uballa. There were no Persian forces at Uballa, and the town was occupied without any resistance.
Hisn ul Mar'at. Muthanna with his column rode ahead of the main Muslim army. The task of this column was to reconnoiter and kill the strugglers left behind the retreating Persians.
North of Zubeir stood a fort known as "Hisn ul Mar'at" - the fort of the lady. A Persian princess Qamarzad who was related to the Persian emperor held it. Muthanna left a contingent under his brother Mu'anna to lay siege to the fort of the lady and himself proceeded with his column further north. Muthanna assaulted the fort and finding the resistance futile, Qamarzad surrendered. She was offered to accept Islam or to pay 'Jizya'. She accepted the first alternative and became a Muslim. Thereupon Mu'anna proposed marriage, and she married him.
The Persian Force. In the meantime another Persian army assembled at al-Madsen. It was placed under the command of a top ranking Persian General, Qarin bin Quryana. Like Hormuz, Qarin was also a 'one hundred thousand dirham' man. The original mission of Qarin was to march with his army to Uballa to reinforce Hormuz.
From al-Madain, the Persian army marched along the left bank of the Tigris. They crossed the Tigris at Mazar, and here they came to know of the defeat of the Persians at Kazima. Qarin camped at Mazar, and soon the remnants of the army of Hormuz who had escaped from Kazima joined the camp. They included the Generals Qubad and Anushjan who had commanded the wings of the army at Hormuz at Kazima.
Qarin was shocked that the imperial army of Persia under such a General as Hormuz should have been defeated by the uncouth Arabs. He resolved that he would avenge the defeat of Kazima and drive the Arabs to the desert.
Khalid's march to Mazar. The advance guard of Muthanna who scoured the countryside came to know of the Persian concentration at Mazar. Muthanna informed Khalid of such concentration. Qarin came to know that some Muslim forces were lurking in the neighborhood, and his plan was to fall on this Muslim force and destroy it, before it could get help from the main Muslim army. Khalid realized the danger that beset the column of Muthanna. Khalid was keen that he should destroy the Persian force under Qarin while the impact of the defeat at Kazima was still fresh in the Persian mind. By forced marches, Khalid reached Mazar in the third week of April 633 C.E. before Qarin could take any action against the column of Muthanna.
Battle of Mazar. Qarin concluded that one of the causes of the defeat of the Persians at Kazima had been that the Muslims had been able to carry flanking maneuvers, which had made the Persians lose their nerve. In order to avoid such a situation at Mazar, Qarin deployed his forces with the main river in the rear so that there may be no possibility of outflanking them.
As Khalid surveyed the situation, he felt that at Mazar, he would have to fight a frontal set piece battle. This was the usual Persian style, and in this respect the advantage lay with the Persians. Khalid, however, hoped that with the blessings of God, he would be able to defeat the Persians at their own game.
Khalid deployed the army with a center and wings. He commanded the center himself, while the wings were commanded by Asim bin Amr and Adi bin Hatim. The Persian army was similarly deployed with Qarin commanding the center, and Qabad and Anushjan commanding the wings.
The battle began with a call to a duel. Qarin stepped forward from the Persian side and gave the challenge. Before Khalid could step forward in response to the challenge, another Muslim commander, Ma'qal bin Al Ashi rode out of the Muslim front to grapple with Qarin. Khalid let Ma'qal have the chance. Ma'qal was an expert swordsman, and he killed Qarin.
As Qarin fell, Qabad and Anushjan stepped forward and gave the challenge for duel. Asim and Adi, commanders of the wings of the Muslim forces, accepted the challenge. In the personal combats that followed, Asim killed Anushjan and Adi killed Qabad.
After the fall of the three Persian Generals. Khalid gave the Muslim forces the order for a general attack. In spite of the demoralization that followed in the deaths of their three top most Generals, the Persian forces fought with great tenacity. Khalid intensified the pressure, and the Persian ranks began to give way. With the increased violence of the Muslim attacks, the Persian army broke up and made for the river.
The retreat of the Persian army soon became a rout. The lightly armed Muslim soldiers soon overtook the heavily equipped Persians and slaughtered them mercilessly. According to the Muslim historian Tabari, 30,000 soldiers were killed in the battle of Mazar. The Muslims won the second victory against the Persians as well.
Consequences of the battle of Mazar. In the battle of Mazar, heavy spoils were won by the Muslims. These exceeded the booty gained at Kazima. Four-fifths of the spoils were distributed among the soldiers and one-fifth share was sent to Madina.
After the victory of Mazar the local inhabitants offered submission and agreed to pay 'Jizya' to the Muslims. Khalid established his headquarters at Hufeir, and a team of Muslim officials was appointed to attend to the administration of the country and collect taxes.