Sahih Bukhari
Fighting for the Cause of Allah (Jihaad)
Volume: 004 / Book Number: 052 / Hadith Number: 286
Narrated 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).