From Sahih Muslim (Hadith 3608):
Abu Sa'id al-Khudri (Allah her pleased with him) reported that at the Battle of Hanain Allah's Messenger (ﷺ) sent an army to Autas and encountered the enemy and fought with them. Having overcome them and taken them captives, the Companions of Allah's Messenger (may peace te upon him) seemed to refrain from having intercourse with captive women because of their husbands being polytheists. Then Allah, Most High, sent down regarding that:" And women already married, except those whom your right hands possess (iv. 24)" (i. e. they were lawful for them when their 'Idda period came to an end)
Reference: Muslim 3608