Preparation of the Persians. After the defeat of the Persians at Mazar, the Persian emperor Ardsheer ordered the assembling of two more Persian armies to fight against the Muslims. One army was placed under the command of Andarzaghar, a military Governor of considerable standing. He had grown up among the Arabs, and was familiar with the Arab way of war. He commanded considerable popularity among the Arab tribes allied with the Persians. In addition to the regular Persian army, Andarzaghar was commissioned to raise contingents from the Arab auxiliaries. The other force was placed under the direct command of Bahman, the Commander-in-Chief of the Persian forces.

Andarzaghar was required to move with his army to grapple with the Muslims. The other force under Bahman was to follow after some time. Andarzaghar set off from al-Madsen and moved along the east bank of the Tigris. He crossed the Tigris at Kaskar, the site where the city of Wasit was founded later. From there he moved southwest to the Euphrates, and after crossing it established his camp at Walaja.

At Walaja, Andarzaghar was joined by the Arab auxiliaries as well as the remnants of the army of Qarin who had escaped from the battlefield of Mazar. The strength of the army of Andarzarghar was very considerable, and if the army of Bahman reinforced it, the Persian army was likely to assume formidable dimensions. Khalid's strategy therefore, was that he should tackle the army of Andarzaghar before the main army under Bahman could join it.

Battle of Walaja. By forced marches, Khalid reached Walaja. As Andarzaghar surveyed the field, the Muslim army did not consist of more than 10,000 persons and the Muslim cavalry was nowhere to be seen. The strength of the Persian army was thrice the strength of the Muslim army, and Andarzaghar thought that in no time he would be able to make mince meat of the Muslim force and thus avenge the defeats of Kazima and Mazar.

The battle at Walaja began as usual with a duel. Out of the Persian ranks stepped forward their champion 'Hazer Mard', the giant of a man supposed to have the strength of a thousand warriors. Khalid stepped forward from the Muslim front to grapple with the giant. Khalid appeared to be no match for the giant, but surprisingly enough after a few minutes of dueling, Khalid struck a heavy blow at his adversary who reeled under the weight of his own heavy body. Khalid repeated the strokes until the giant was dead.