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. (ES)
English reference (ES): Book 11, Hadith 1314 (ES)
Arabic reference (ES): Book 11, Hadith 1287 (ES)