The Muslim army besieging Damascus was divided into five corps each under a Commander. Each corps was required to guard one or two gates of the city. In the north there were two gates, namely the Thomas gate, and Paradees gate. The corps commanded by Shurahbil was stationed outside Thomas gate, while the corps commanded by Amr bin Al Aas was posted outside Paradees gate. In the east there was one gate. Here corps commanded by Khalid himself was posted. In the south there were two gates. Here the corps commanded by Yazid was posted to look after both the gates. In the west there was one gate, namely the Jabiya gate. Here the corps commanded by Abu Ubaida was posted. The Byzantine force within the fort was commanded by Thomas who was a son-in-law of the Byzantine emperor Heraclius.
Thomas counted on the arrival of a relief force to be sent by Heraclius. When Thomas came to know that the relief force had been battered at Bait Lihya, he decided to sally forth from the fort and break through the besieging Muslim forces. On a September day mustering a strong force, Thomas broke out through the Thomas gate in the north. Here he was opposed by the force led by Shurahbil. There was an exchange of shots leading to casualties on both sides. On the Muslim side, one of the soldiers killed was Aban bin Saeed bin Al Aas. He had only been married a few days ago. As soon as his widow came to know of his death, she donned his uniform, took a bow and joined the Muslim archers, determined to seek revenge for the death of her husband.
The Byzantine soldiers rushed out of the Thomas gate and launched an attack on the Muslims. There was heavy fighting. Shurahbil's corps was outnumbered, but the Muslims held their ground. Thomas commanded the Byzantine forces personally. In order to demoralise the Muslim forces, Thomas rushed forward to overpower the Muslim Commander Shurahbil. Before Thomas could reach Shurahbil, an arrow shot by the widow of Aban struck him. That made the Byzantines fall back to the fort leaving behind a large number of the dead.
The following night, the Byzantines sallied forth from all the gates simultaneously. There was hard fighting. The Byzantines tried their best to break through the Muslim forces. The Muslim forces withstood their ground seeing that there was no weakening in the Muslim front, the Byzantines returned to the fort, leaving hundreds of their soldiers dead on the battle-lield.
The following day a young Greek Jonah by name slipped from the fort, and coming to the Muslim camp sought an audience of Khalid. He said that he was madly in love with a girl with whom he had been married, but the ceremony of handing over the bride had not taken place. He had asked his father-in-law to perform the ceremony but he wanted him to wait till the war was over Jonah stipulated that if the Muslims could help him in getting his bride, he would help the Muslims in winning the fort. Khalid promised to help, and Jonah the Greek youth pointed a place on thc city walls which the Muslims could scale. That night Khalid and a picked band of his soldiers scaled the wall and entered the fort. Then they made for the gate and broke it open. Through the gate the Muslim army rushed in, and began to massacre the Byzantines .
When Thomas came to know of the entry of Khalid through the eastern gate, he waited on Abu Ubaida at the western gate, and offered surrender on the usual terms of paying Jizya. Abu Ubaida accepted the surrender and offered amnesty to the Byzantines. When the forces of Abu Ubaida entered the city from the western gate they soon found that Khalid had already entered it from the eastern gate. Khalid and Abu Ubaida met in the heart of the town. Abu Ubaida told Khalid that the Byzantine Commander had surrendered and that he had offered the Byzantines amnesty. Khalid said that he had won Damascus and there was no question of allowing amnesty. A council of war of the Muslim Generals met, and it was ultimately decide that the guarantee given by Abu Ubaida should be respected.
The Byzantines were allowed to move out of the fort. They were allowed to carry their belongings. It was further stipulated that there would be no pursuit for three days.
Jonah met his girl, and wanted her to come to him. She wanted him to accompany them on their flight from Damascus. He told her that he had become a Muslim and that he would stay in Damascus. Thereupon she refused to have any deal with him.
All the Byzantines left the fort, which was thereafter occupied by the Muslims. The Muslims conquered Damascus some time towards the end of September 634 A.D.