From Yamamah to Yarmuk

After the Prophet's ﷺ death, Abu Bakr sent Khalid against the tribes who had apostatised or refused the zakah, and against the false prophets. At Yamamah, against the followers of Musaylimah, a hard-fought battle ended with Musaylimah's death and a heavy toll among the Qur'an reciters, which led to the first compilation of the Qur'an.

Abu Bakr then sent Khalid to Iraq. There he won a series of engagements against the Persians and the Arab tribes allied with them, including at al-Hirah. Then, with Abu Bakr's order, he led his men across the Syrian desert in a famous forced march of several days, to reinforce the army in Syria.

At Yarmuk in 15 AH, he commanded the Muslim cavalry and had a decisive part in the battle against the Byzantine army, which ended Byzantine rule in Syria. It was said that he was never defeated in all his battles. Abu Bakr is said to have remarked that the mothers of the Quraysh would not bear the like of Khalid.