﴿ إِلَّا عَلَىٰٓ أَزْوَٰجِهِمْ أَوْ مَا مَلَكَتْ أَيْمَٰنُهُمْ فَإِنَّهُمْ غَيْرُ مَلُومِينَ ﴾

“[not giving way to their desires] with any but their spouses - that is, those whom they rightfully possess [through wedlock]: for then, behold, they are free of all blame,”

except from their spouses that is to their spouses and what slaves their right hands possess that is concubines for then they are not blameworthy in having sexual intercourse with them.