Sahih Bukhari Volume 009, Book 089, Hadith Number 299.
Narrated By Ibn 'Umar : The Prophet sent (an army unit under the command of) Khalid bin Al-Walid to fight against the tribe of Bani Jadhima and those people could not express themselves by saying, "Aslamna," but they said, "Saba'na! Saba'na! " Khalid kept on killing some of them and taking some others as captives, and he gave a captive to everyone of us and ordered everyone of us to kill his captive. I said, "By Allah, I shall not kill my captive and none of my companions shall kill his captive!" Then we mentioned that to the Prophet and he said, "O Allah! I am free from what Khalid bin Al-Walid has done," and repeated it twice.