March to Iraq. In March 633 C.E. when Khalid bin Walid was quartered with his army at Yamama, he received orders from Abu Bakr that he should march to Iraq and start operations in the region of Uballa where the two rivers, the Tigris and the Euphrates, met. Four other columns each under the command of Muthanna, Mazar, Harmala, and Salma were also directed to proceed to Iraq to reinforce the main Muslim army under the command of Khalid bin Walid.
Hormuz. Uballa was the main port of Iraq and was the headquarter of the district then known as 'Dasht Meisan'. Uballa being a junction of many land routes was the gateway of Iraq and commanded great strategical importance. The Governor of the district was Hormuz, a veteran General and a skilful administrator. In the Persian administrative hierarchy, he held 'one hundred thousand dirham' rank, and was entitled to wear a gem studded cap worth one hundred thousand dirhams. He was an imperialist, very haughty and arrogant. He held the Arabs in contempt. His harshness and high handedness became the subject of a saying among the local Arabs "More hateful than Hormuz".
Khalid's letter to Hormuz. As soon as Khalid received orders to march to Iraq, he addressed a letter to Hormuz calling upon him to accept Islam. The letter read: "Submit to Islam and be safe. In the alternative you may agree to the payment of 'Jizya', and you and your people will be under our protection. Otherwise you will have only yourself to blame for the consequences for I bring a people who desire death as ardently as you desire life."
Preparations of Hormuz. Hormuz mustered his forces and set out from Uballa to meet the Muslim forces. On the direct route from Uballa to Yamama the first stage was Kazima, and Hormuz decided to give a battle to the Muslims at that place. His idea was that the Muslim forces should be kept away from Uballa. On arrival at Kazima, Hormuz deployed his army with a center and two wings, the right and the left. His men were linked together with chains, and in this state of affairs the Persians awaited the arrival of the Muslim forces.
Tactics of Khalid. Khalid gave a slip to the Persians, and instead of following the direct route to Uballa via Kazima, he followed the indirect route via Hufeir. Hufeir was much closer to Uballa than Kazima, and when Hormuz came to know that Khalid had already reached Hufeir, he was very much upset. He immediately ordered his forces to march to Hufeir. It was a weary two days march for the Persian forces, but when they reached Hufeir they found that the Muslim forces had left for Kazima. The Persians had no option but to march back to Kazima.