'Ein-at-Tamr. Khalid left a garrison at Anbar under the command of Zabarqan bin Badr, and himself marched further afield with the main Muslim army. In early August 633 C.E., the Muslim army recrossed the Euphrates, and marched southward. This time his objective was 'Ein-at-Tamr. 'Ein-at-Tamr was a large fortified town surrounded by date palms. 'Ein-at-Tamr in fact meant 'Spring of dates'. It was a place of strategical importance, and was garrisoned by Persian forces and the Arab auxiliaries.

Christian Arabs. The Persian forces at 'Ein-at-Tamr were commanded by Mehran bin Bahram Jabeen who was a skillful military commander. The Christian Arabs belonged to the tribe of Namr, and were led by their chief Aqqa bin Abi Aqqa. Aqqa was a man of formidable dimensions and enjoyed great reputation for his prowess. He was a devout Christian and was very hostile to Islam.

Aqqa was proud of his bodily strength and Arab lineage. In a war council with Mehran, Aqqa volunteered to fight against the Muslims with his men. He argued "Diamond cuts diamond, and we Christian Arabs know best as to how to fight against the Muslim Arabs. Let us fight against the Muslims in the first instance". Mehran accepted the offer and said, "You are right; you are the best men to fight against the Muslims. Go ahead, and give the Muslims a tough fight. We will remain close to you, and will come to your assistance, when you need reinforcement."

Battle of 'Ein-at-Tamr. The Persian forces remained at 'Ein-at-Tamr, but the Christian Arab auxiliaries under the command of Aqqa marched on the road to Anbar to intercept the advance of the Muslim force under Khalid. The two forces met at a distance of some ten miles from Ein-at-Tamr. As soon as the two forces came in sight, they went in for action immediately. Khalid deployed the Muslim forces in the usual way, the center and the wings. Khalid had heard of the boastings and vaunts of Aqqa, and the plan of Khalid was to take Aqqa captive alive. Aqqa led the center of his force, and with his heavy body he looked very defiant. When the battle began, the wings of the Muslim army charged with considerable vehemence, but the center under the direct command of Khalid charged in a luke-warm way. That gave Aqqa the impression that the center of the Muslim army was showing signs of exhaustion. He decided to avail of this advantage. He launched an attack at the central wing of the Muslim force with considerable vehemence. Before this attack, the Muslim center withdrew. That made the central wing of Aqqa's force rush forward. Such impetuous advance cut off the central wing of Aqqa's force off from the other wings of the army of the Christian Arabs. At this stage the Muslim force turned a somersault, and launched a furious charge enveloping the forces of Aqqa. In the hand to hand fighting that followed, the men surrounding Aqqa were cut to pieces, and Aqqa was captured alive according to plan.

Occupation of 'Ein-at-Tamr. With the capture of Aqqa, the Christian Arabs lost nerve, and fled to 'Ein-at-Tamr, hoping to be reinforced by the Persian forces. When the Arab fugitives reached 'Ein-at-Tamr, they found that the Persian forces under Mehran had already evacuated the town, and left for Al-Madain. Finding themselves abandoned and betrayed the Christian Arabs rushed into the fort, closed the gates and prepared for a siege.

The Muslims soon arrived at 'Ein-at-Tamr, and laid siege to the fort. Aqqa and other prisoners in the Muslim camp were paraded outside the fort, and that had an unnerving effect on the defenders. The Christian Arabs soon asked for terms, but Khalid said that there would be no terms and that the surrender must be unconditional. After a few days the resistance of the Christian Arabs broke down, and they surrendered unconditionally. Aqqa and the leaders of the Christian Arabs were beheaded. The people agreed to pay Jizya. A huge booty was collected and distributed according to the usual formula.

Monastery at 'Ein-at-Tamr. At 'Ein-at-Tamr was a monastery where boys were trained for priesthood. These boys were converted to Islam. Among these boys was one Naseir whose son Musa later became the Governor of Africa, and the Conqueror of Spain.