Musnad Ahmad 1:42

'Ali ibn 'Ayyash narrated to us, al-Walid ibn Muslim narrated to us, Wahshi ibn Harb ibn Wahshi ibn Harb narrated to me, from his father, from his grandfather Wahshi ibn Harb: That Abu Bakr, may Allah be pleased with him, commissioned Khalid ibn al-Walid to fight the people of apostasy and said: "I heard the Messenger of Allah, peace and blessings of Allah be upon him, saying: 'An excellent servant of Allah and brother of the clan is Khalid ibn al-Walid, and a sword from the swords of Allah, which Allah the Exalted and Majestic drew against the disbelievers and the hypocrites.'"