With Emesa already in hand, Abu Ubaidah and Khalid moved towards Chalcis, which was strategically the most significant Byzantine fort. Through Chalcis the Byzantines would be able to guard Anatolia, Heraclius' homeland of Armenia, and the regional capital, Antioch. Abu Ubaidah sent Khalid with his mobile guard towards Chalcis. The virtually impregnable fort was guarded by Greek troops under Menas, reportedly second in prestige only to the Emperor himself. Menas, diverting from conventional Byzantine tactics, decided to face Khalid and destroy the leading elements of Muslim army before the main body could join them at Hazir 5 kilometres east of Chalcis.

The battle was still in its early stages when Menas was killed. As the news of his death spread among his men, the Byzantine soldiers went wild with fury and savagely attacked to avenge their leader's death. Khalid took a cavalry regiment and maneuvered from the side of one of the wings to attack the Byzantine army from the rear. Soon the entire Roman army was encircled and defeated. It is said that Menas and his garrison had never suffered such a severe defeat.

The resulting Battle of Hazir even reportedly forced Umar to praise Khalid's military genius, saying, "Khalid is truly the commander. May Allah have mercy upon Abu Bakr. He was a better judge of men than I have been.