Sahih Bukhari Volume 4, Book 52, Hadith Number 286.

Narated By Salama bin Al-Akwa : “An infidel spy came to the Prophet while he was on a journey. The spy sat with the companions of the Prophet and started talking and then went away. The Prophet said (to his companions), ‘Chase and kill him.’ So, I killed him.” The Prophet then gave him the belongings of the killed spy (in addition to his share of the war booty).