March to Ajnadein. From Damascus and other parts of Syria, the Muslim forces marched to Ajnadein, and there camped at some distance from gigantic camp of the Byzantines.
Khalid's address. The total strength of the Muslim army was 40,000, while the strength of the Byzantine army was over one hundred thousand. The odds appeared to be against the Muslims, but Khalid had firm faith in God. He inspected the ranks, and addressed the Muslim warriors thus: "O Comrades-in-arms, you are to face the biggest army that the Byzantines could muster. Should you come out of the battle victorious all is yours. Fight in good earnest and remain steadfast to the teachings of Islam. See that you do not turn back for God sees you. Close your ranks, keep your heads, and do not lose heart."
Khalid's address to women contingent. Halting before the women's contingent in the Muslim army, Khalid said: "Sisters-in-faith, make sure that your actions be acceptable to Allah and His prophet. Your participation in this war will go down in history, and I know that you will acquit yourself honorably. Should the Byzantines attack you, show your mettle and the heroic stuff you are made of. Should you find any Muslim fleeing from the field, reproach him until he turns again to face the enemy. It is by these means that you will infuse the menfolk with a spirit that can stand up against the heaviest odds."
Zarrar. Khalid sent Zarrar on a reconnaissance mission. He stripped himself to the waist and rode up to the center of the Byzantine camp. Here he was seen by the Byzantines, and a body of thirty Byzantine soldiers rode out to catch him. Zarrar killed nineteen of the Byzantine soldiers before the survivors turned and galloped back to their camp. In the Byzantine camp, Zarrar became a legend for daredevilry.
The Byzantine spy. The Byzantines sent a Christian Arab to the Muslim camp to get information about the strength and quality of the Muslim forces. The spy then went back in the Byzantine camp reported about the Muslims in the following terms: "By night they are like monks; by day they are like warriors. If the son of the ruler were to commit theft, they would cut off his hand, and if he were to commit adultery, they would stone him to death."
On getting this report, Qubuqlar the Deputy Commander of the Byzantine forces declared: "If whet you say is true, it would be better to be in the belly of the earth than to meet such people upon its surface. "
Commencement of the battle of Ajnadein. The battle of Ajnadein began on 30th July 634 C.E. The Muslim army was deployed on a front of about five miles. Thc center was placed under M`uadh bin Jabal; the right wing was placed under Saeed bin 'Amir; while, the left wing was placed under Abdur Rahman the son of the Caliph Abu Bakr. Khalid commanded the force as a whole, and he kept a reserve with him who could be commissioned for special jobs. This reserve included among others: 'Amr bin Al Aas; Zarrar; Rafe' and Abdullah the son of Umar.
Peace offer of the Byzantines. The Byzantines took the battle position about half a mile away from the Muslim front line. Before the battle began, a venerable old man dressed in black emerged from the Byzantine ranks and walked up half way towards the Muslim army. Khalid stepped forward to meet him. Addressing Khalid, the Byzantine bishop said: "Lo', we have an army numerous as the atoms, and it is not like the armies you have met before. With this army, Caesar has sent his mightiest Generals. My master is nevertheless inclined to be generous with you. Withdraw and we will give each of you a dinar, a robe, and a turban, and for you there will be a hundred diners, hundred robes, and hundred turbans."
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.