Sahih Bukhari Volume 5, Book 59, Hadith Number 636.

Narrated By Al-Bara : Allah’s Apostle sent us to Yemen along with Khalid bin Al-Walid. Later on he sent Ali bin Abi Talib in his place. The Prophet said to ‘Ali, “Give Khalid’s companions the choice of either staying with you (in Yemen) or returning to Medina.” I was one of those who stayed with him (i.e. Ali) and got several Awaq (of gold from the war booty.