Sahih Muslim
The Book on Government (Kitab Al-Imara)
Book Number: 020 / Hadith Number: 4670
It has been narrated on the authority of Abu Sa'id Khudri that the Messenger of Allah (may peace be upon him) sent a force to Banu Lihyan (who are from Banu Hudhail, and said: One man from every two and the reward (will be divided) between the two.