"We got some captives on the day of Awtas, and they had husbands among their peopled. They mentioned that to the Messenger of Allah, so the following was revealed: And women who are already married, except those whom your right hands posses.  

أَصَبْنَا سَبَايَا يَوْمَ أَوْطَاسٍ وَلَهُنَّ أَزْوَاجٌ فِي قَوْمِهِنَّ فَذَكَرُوا ذَلِكَ لِرَسُولِ اللَّهِ ﷺ فَنَزَلَتْ (وَالْمُحْصَنَاتُ مِنَ النِّسَاءِ إِلاَّ مَا مَلَكَتْ أَيْمَانُكُمْ )