It was narrated from Wahshi bin Harb that Abu Bakr appointed Khalid bin al-Waleed as commander to fight the apostates and he said:
I heard the Messenger of Allah (ﷺ) say: “What a good slave of Allah and member of the tribe Khalid bin al-Waleed is! [He is] one of the swords of Allah that Allah, may He be glorified and exalted, has unsheathed against disbelievers and hypocrites.`