Samurah (RAA) narrated that The Messenger of Allah (ﷺ) said:
"Kill the mature men of the polytheists but spare their children." Related by Abu Dawud and At-Tirmidhi graded it as Sahih. (ID)
English reference (ID): Book 11, Hadith 1314 (ID)
Arabic reference (ID): Book 11, Hadith 1287 (ID)