Khalid repudiating the peace offer said: "We have not come here to accept alms. Your choice is either to accept Islam or pay Jizya. The third alternative is sword. We are not afraid of the strength of your army, our one man may fight against ten of your men."

The first day of the battle. The battle began with personal combats. From the Muslim camp, Zarrar stepped forward, and he gave the battle cry: "I am the death of the pale ones; I am the killer of the Byzantines; I am a scourge sent for you; I am Zarrar bin Al Azwar."

All the Byzantine champions who came forward to meet the challenge of Zarrar were killed by him. These included three Byzantine Generals. Thereafter, Khalid ordered a charge, and the entire Muslim front dashed forward hurling itself at the Byzantine army. The battle raged furiously for several hours. By the evening, both sides broke contact, and fell back to their original lines.

Werdan's conspiracy. Werdan, the Commander-in-Chief of Byzantines, was distressed that on the first day of the battle, thousands of Byzantines had been killed, while the casualties on the Muslim side were very few. Werdan was overawed by Khalid, and he felt that as long as Khalid was there to command the Muslim forces, there was little chance for the Byzantines to win a victory. He accordingly hatched a plot to ambush Khalid.

A Christian Arab was sent to Muslim camp with a message from Werdan that Khalid should meet him for peace parleys. So great was the awe of Khalid that the emissary disclosed the details of the plot Werdan had hatched, and indicated the spot where under the instructions of Werdan, the Byzantines were to lie concealed to fall upon Khalid unawares.

Death of Werdan. The next day as the two armies again took the field; Khalid and Werdan stepped forward to negotiate peace parleys. Werdan desired that the Muslim force should withdraw, and they could have some money. Khalid ridiculed the offer and said that in case the Byzantines did not accept Islam or pay Jizya, the sword alone would decide the issue. Thereupon, Werdan gave the signal, and from behind the hillock emerged ten warriors dressed in Byzantine uniforms. As they came forward, Khalid saw that they were Zarrar and his companions. They had killed the Byzantine soldiers sent by Werdan and had donned their uniforms. Zarrar, at once, fell on Werdan and severed his head with his sword.

The Muslim victory. With the death of Werdan, the Muslims launched the attack. The Muslims struck violently, and the Byzantines struggled desperately to hold the assault. Then Khalid brought in his reserves. That turned the tide of the battle. The Muslims drove deep wedges into the Byzantine army. Some Muslim soldiers advanced and killed Qaubuqlar who commanded the Byzantine forces after the death of Werdan. With the death of Qubuqlar, the Byzantine lost heart and fled from the battlefield. The Muslim cavalry pursued the fugitives and the Byzantines were slaughtered in thousands. The Muslims won a complete victory. The large Byzantine army at Ajnadein was practically annihilated.

Report of the battle. Khalid sent a detailed report of the Muslim victory to Abu Bakr along with the state share of the booty. At the battle of Ajnadein over 50,000 Byzantine soldiers died against 450 Muslims only. At Madina the news of the victory was received with great joy. Abu Bakr lay ill, and this good news cheered him up.