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