Khalid ibn al-Walid went with the Muslims accompanying him to Firaz, where the borders of Syria, Iraq, and Jazira converge. He spent the month of Ramadan there. Because he was occupied with the enemy, he did not fast. When the Byzantines heard that Khalid had come there and settled in a place close to their homeland, they were stirred to zeal and became enraged. They gathered a large number of soldiers. They aided the tribes of Taghlib, Iyad, and Tamr. Then they advanced upon Khalid. Between them and Khalid was the Euphrates River. The Byzantines said to Khalid:
– Cross the Euphrates and come over to us. Khalid replied to them:
– No, you cross the Euphrates and come over to us, he said. The Byzantines crossed the river and came to face the Muslims. This event took place in the month of Dhu al-Qa'da in the twelfth year of the Hijra. The two sides fought fiercely. Then Allah, the Exalted, routed the Byzantine forces. The Muslims found the opportunity to pursue and chase them. In this battle, the Muslims killed 100,000 of the enemy. After this battle, Khalid stayed at Firaz for ten days. Then he announced that they would return to Hira. Five days before the end of Dhu al-Qa'da, they returned to Hira. Khalid ordered that Asim ibn Amr be at the head of the vanguard, and Shajara ibn Eazz at the head of the rearguard. Khalid gave the impression that he was going with the rearguard. He himself, however, turned towards the Sacred Mosque (Masjid al-Haram) with a few companions. He went to Mecca by a route he had not taken before. That year, he performed the pilgrimage (hajj). Then he returned and reached the troops before the rearguard arrived at Hira, and that year, no one except a few of his companions knew that he had performed the pilgrimage. Abu Bakr al-Siddiq only realized that he had performed the pilgrimage after Khalid returned from it. He sent him a letter reproaching him for separating from his army. As a penalty, he ordered him to leave Iraq and go to Syria and fight there. In the letter he sent, he said to Khalid:
"The communities did not prevail by being absent, but only by Allah's help, O Abu Sulayman (Khalid's kunya was Abu Sulayman). May your intention and your share be blessed for you. Complete what you have begun so that Allah may complete it for you. Do not become proud because of what you have done, lest you suffer loss and be left without help. Do not act coyly because of what you have accomplished. For gratitude (minna) belongs only to Allah. Reward and recompense are things that He alone bestows."