Musannaf Ibn Abi Shayba 27:626

Husayn ibn Ali narrated to us, from Za'idah, from Abd al-Malik ibn Umayr, who said: Umar sent Abu Ubaydah to al-Sham and dismissed Khalid ibn al-Walid. Khalid ibn al-Walid said: "The trustee of this nation has been sent over you." Abu Ubaydah said: "I heard the Messenger of Allah, may Allah bless him and grant him peace, say: 'Khalid ibn al-Walid is a sword from the swords of Allah, and an excellent young man of the tribe.'"