On the fifth day the two armies again lined up for action, but there was no assault. Then an emissary came forward from the Byzantine side proposing a truce for the next few days so that fresh negotiations could be held. The Muslims did not accept the proposal. They said that they were in a hurry to finish the business. That day there was no battle.
On the sixth day before the battle began' Gregory a General of the Byzantine army stepped forward and challenged the Muslim Commander-in-chief to a duel. Abu Ubaida accepted the challenge. In the duel, Abu Ubaida killed Gregory.
Thereafter Ahu Ubaida gave the signal for a Muslim attack, and the Muslim front surged forward. The Muslim cavalry led by Khalid intensified their blows against the Byzantine cavalry, and after a hard struggle the Byzantine cavalry was driven away from the field. The Byzantine infantry was now left without the support of the cavalry. By a flanking movement, Khalid attacked the Byzantines both from the front as well as the rear, and so no sectors of the Byzantine army collapsed. The Byzantine infantry was now in full retreat, and the Muslims suffered it to retire.
The Byzantines retreated towards Qadi-ur-Raqqad. Here a Muslim contingent under Zarrar lay ambushed and they made mince meat of the flying Byzantines.
By the afternoon of the sixth day of the battle only a third of the Byzantine army remained in the battle-field; the rest had fled away. The Muslim army now fell on the Byzantiaes.
In the meantime a storm began to blow. It blew against the faces of the Byzantines, and provided a greater momentum to the Muslims to rush forward. In the confusion that followed the Byzantines lost their bearings. Panic stricken they fled, and the pursuing Muslims killed thousands of Byzantines right and left. The battle of Yermuk ended in a great victory for the Muslims.
The Byzantine Commander-in-chief, Mahan with the remnants of his army fled towards Damascus. The Muslims pursued them, and overtook them a few miles short of Damascus. The Muslims attacked the Byzantine rearguard with great violence. In the scuffle that followed Mahan was killed. Many Byzantines were slaughtered, but some managed to escape to tell Heraclius the story of the disaster that the Byzantines had met at the battle-field of Yermuk.
The battle of Yermuk was the greatest battle that the Muslims had fought so far. That spelled the end of the Byzantine rule in Syria, and ushered in the Muslim rule.