From Sahih Bukhari (Hadith 3051):
Narrated Salama bin Al-Akwa`:"An infidel spy came to the Prophet (ﷺ) while he was on a journey. The spy sat with the companions of the Prophet (ﷺ) and started talking and then went away. The Prophet (ﷺ) said (to his companions), 'Chase and kill him.' So, I killed him." The Prophet (ﷺ) then gave him the belongings of the killed spy (in addition to his share of the war booty)
Reference: Bukhari 3051