Quran 4:24 And Sahih Muslim Book 8, Hadith Number 3432
Quran 4:24 relates to women prisoners (‘ Jangi Qaidi ’) who chose to marry Muslim men out of their freewill . This has nothing to do with slaves, it relates to the situation where already married women were captured during war, in that case, if they chose to marry any other man, they were given exception that they can if they chose to do so, in accordance with the already held custom of Arabs where previous Nikah was considered ineffective, as soon as a married woman became a war captive. There is a difference between a prisoner of war and a Slave. Islam closed all doors to slavery and forbid making of new slaves in Quran 47:4 , so there was no question of turning prisioners of wars to slaves. As for current slaves, a gradual approach was adopted where current slaves were given an option to choose between slavery and freedom as per their own circumstances. There were only three exceptions to this rule: i ) Captives who were slaves prior to their capture and, at certain instances, were distributed among people as slaves were an exception and the directive stated in the verse (47:4) never related to them. ii ) Brutal adversaries, as per the dictates of the law of ‘اتمام الحجة’ (itmam-ul-hujjah) , were required to be slain wherever found. iii ) The captives of the Banu Qurayzah who met a fate decided by an arbitrator appointed by themselves : their men were slain and their women and children were sold as slaves. Please also refer to the video below from 12:02 to 13:40 https://youtu.be/hLYwl2NB3Ao?t=722