﴿ ٱلَّذِينَ يُظَٰهِرُونَ مِنكُم مِّن نِّسَآئِهِم مَّا هُنَّ أُمَّهَٰتِهِمْ ۖ إِنْ أُمَّهَٰتُهُمْ إِلَّا ٱلَّٰٓـِٔى وَلَدْنَهُمْ ۚ وَإِنَّهُمْ لَيَقُولُونَ مُنكَرًۭا مِّنَ ٱلْقَوْلِ وَزُورًۭا ۚ وَإِنَّ ٱللَّهَ لَعَفُوٌّ غَفُورٌۭ ﴾

“As for those of you who [henceforth] separate themselves from their wives by saying, “Thou art as unlawful to me as my mother”, [let them bear in mind that] they can never be [as] their mothers: none are their mothers save those who gave them birth: and so, behold, they but utter a saying that runs counter to reason, and is [therefore] false. But, behold, God is indeed an absolver of sins, much-forgiving:”

Saying to one’s wife, ‘To me you are like my mother’s back’. This was an old pagan custom which was known as zihar, by which one’s wife could be wrongfully divorced.