Campaign against Busra. Over running the southern frontier posts, Abu Ubaida and Shurahbil occupied the Hauran district lying east of the river Yermuk, with a view to guarding against a surprise attack from Busra, Abu Ubaida dispatched a detachment of four thousand warriors under Shurahbil to capture Busra.
Khalid's march to Busra. At Marj Rahit, Khalid came to know that a Muslim detachment was fighting at Busra. Bypassing Damascus, Khalid and his army set off for Busra. Khalid sent a message to Abu Ubaida, the Commander-in-Chief of the Muslim forces in Syria that he should meet him at Busra.
Khalid's arrival at Busra. At Busra the Muslim forces were heavily outnumbered. Taking advantage of their numerical strength, the Byzantines launched a vigorous attack, and under the intensity of the attack, the Muslim forces began to reel back. The position for the Muslims became critical, and Shurahbil prayed to God for help. Miraculously the army of Khalid arrived at the scene at the nick of time. That turned the tide of the battle. Seeing that the Muslims had received reinforcement, the Byzantine garrison withdrew to the city and shut its gates.
Commencement of the battle. The following day, the two armies faced each other in battle array. The battle was preceded by a call for personal combat between the Commanders of the armies. Khalid stepped forward from the Muslim ranks and out of the Byzantine ranks their commander Romanus stepped forward. Before dueling, Khalid offered Islam to Romanus, and surprisingly enough, Romanus after asking a few questions about Islam, declared the article of faith and became a Muslim. He crossed over to the Muslim camp.
Romanus. From the Muslim camp, Romanus addressed the Byzantines in the following terms: "O ye, enemies of God and His prophet. You must not forget that I have accepted the true faith of Islam to please God. Now no common ties exist between you and me, either in this world, or in the world hereinafter. I deny him who was crucified, and sever any connections with his followers. I choose Allah for my Lord, and Muhammad (peace be on him) as my Prophet, the Ka'aba as my sanctuary, and the Muslims as my brethren. In sooth, I bear witness that there is no God but Allah. He has no partner, and Muhammad (peace be on him) is His prophet, whom He selected to direct mankind to the right way. I am fully convinced that God would exalt the true religion of Islam over the religion of those who join partners with His Divinity."
Muslim occupation of Busra. The conversion of Romanus to Islam unnerved the Byzantine forces, and instead of giving the fight, they withdrew to the city and shut the gates against the Muslims. That night, Romanus led a Muslim detachment to a subterranean passage under the ramparts of the city. This contingent was led by Abdur Rahman, the son of Abu Bakr. This contingent entered the city through the underground passage and then dashing towards the city gates opened them for the main Muslim army to enter. The Muslim forces attacked right and left raising the cries of "Allah-o-Akbar." The Byzantines were slaughtered in thousands and the survivors laid down arms. The citizens of Busra agreed to pay Jizya, and thereupon a peace pact was drawn up.
Consequences of the conquest of Busra. The conquest of Busra in the second week of July 634 C.E. was the first important victory gained by the Muslims in Syria. The Muslims lost 130 men in the battle, while the Byzantines lost several thousand persons. Khalid informed Abu Bakr of the viceroy and dispatched the usual one fifth of the spoils of war. The conquest of Busra opened for the Muslims the gate for the conquest of Syria.
Abu Ubaida. At Busra, Abu Ubaida came to meet Khalid. Khalid had replaced him in the over all command of the Muslim forces in Syria, but Abu Ubaida had no grudge on that score. Addressing Khalid, he said, "O father of Sulaiman, I have received with gladness the letter of Abu Bakr appointing you as the Commander-in-Chief. There is no resentment in my heart over this, for I know of your skill in matters of war". Addressing Abu Ubaida, Khalid in reply said, "By Allah, but for the necessity of obeying the orders of the Caliph I would never have accepted the command over you. You are much higher than me in Islam. I am a companion of the Holy Prophet, while you are one whom the Messenger of Allah called the 'trusted one of the nation'."