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.
After the death of 'Hazer Mard', the Muslim army advanced for a general attack. The two armies met with a clash of steel, and the battle raged with unabated fury. The Muslims struck at the heavily armed Persians, but the Persians stood their ground, and repulsed all attacks. Then Andarzaghar ordered a counter attack. The Muslims were able to hold the attack for some time, but as the Persians intensified their pressure, the Muslims began to lose ground and fell back. Andarzaghar exhorted his men to step up their pressure for victory was very much in sight.
At that critical juncture, Khalid gave a signal. The next moment over the crest of the ridge that stretched behind the Persian army appeared columns of mounted Muslim warriors. Raising shouts of 'Allah-o-Akbar', the Muslim cavalry charged at a gallop, and the plain of Walaja shook under the thundering hooves of the Arab horse.
The Persians who were pressing forward were now caught in a trap. When they turned their face to meet the charge of the Muslim cavalry, the main Muslim army delivered a furious charge. The ring of steel became tighter round the Persians and in whatever direction they turned they were struck down by sword and dagger.
The battlefield of Walaja became a slaughterhouse for the Persians. The very helplessness of the Persians excited the Muslims to greater violence. The bulk of the Persian army was annihilated. Andarzaghar fled from the battlefield and penetrated deep into the desert where he lost his way and died of thirst. The battle of Walaja ended in a victory for the Muslims. That was the third consecutive victory of the Muslims over the Persians.
Consequences of the battle of Walaja. The victory of Walaja established the superiority of the Muslim fighting forces. Once again a large booty fell into the hands of the Muslims. Four-fifth of the spoils were distributed among the Muslim warriors on the spot, and the remaining one-fifth were sent to Madina. As the news of the Muslim victory reached Madina, Abu Bakr offered special prayers of thanksgiving to Allah.