The law of God that permits sexual relations only between a man and a woman who are married to each other is part of what defines the marriage arrangement.
وَهِيَ تَقُولُ إِنَّ ٱلْعَلَاقَاتِ ٱلْجِنْسِيَّةَ يَجِبُ أَنْ تَكُونَ مَحْصُورَةً بَيْنَ رَجُلٍ وَٱمْرَأَةٍ مُتَزَوِّجَيْنِ .‏