The Holy Quran, Chapter Al-Qari'a - القارعة

وَالْمُحْصَنَاتُ مِنَ النِّسَاء إِلاَّ مَا مَلَكَتْ أَيْمَانُكُمْ كِتَابَ اللّهِ عَلَيْكُمْ وَأُحِلَّ لَكُم مَّا وَرَاء ذَلِكُمْ أَن تَبْتَغُواْ بِأَمْوَالِكُم مُّحْصِنِينَ غَيْرَ مُسَافِحِينَ فَمَا اسْتَمْتَعْتُم بِهِ مِنْهُنَّ فَآتُوهُنَّ أُجُورَهُنَّ فَرِيضَةً وَلاَ جُنَاحَ عَلَيْكُمْ فِيمَا تَرَاضَيْتُم بِهِ مِن بَعْدِ الْفَرِيضَةِ إِنَّ اللّهَ كَانَ عَلِيماً حَكِيماً

And all married women (are forbidden unto you save those (captives) whom your right hands possess. It is a decree of Allah for you. Lawful unto you are all beyond those mentioned, so that ye seek them with your wealth in honest wedlock, not debauchery. And those of whom ye seek content (by marrying them), give unto them their portions as a duty. And there is no sin for you in what ye do by mutual agreement after the duty (hath been done). Lo! Allah is ever Knower, Wise.