The Quran

ما جَعَلَ اللَّهُ لِرَجُلٍ مِن قَلبَينِ في جَوفِهِ ۚ وَما جَعَلَ أَزواجَكُمُ اللّائي تُظاهِرونَ مِنهُنَّ أُمَّهاتِكُم ۚ وَما جَعَلَ أَدعِياءَكُم أَبناءَكُم ۚ ذٰلِكُم قَولُكُم بِأَفواهِكُم ۖ وَاللَّهُ يَقولُ الحَقَّ وَهُوَ يَهدِي السَّبيلَ

(Saheeh International)

Allāh has not made for a man two hearts in his interior. And He has not made your wives whom you declare unlawful¹ your mothers. And He has not made your claimed [i.e., adopted] sons your [true] sons. That is [merely] your saying by your mouths, but Allāh says the truth, and He guides to the [right] way.

By the expression "You are to me like the back of my mother." Such an oath taken against approaching one's wife was a pre-Islāmic practice declared by Allāh (subḥānahu wa ta‘ālā) to be a sin requiring expiation as described in 58:3-4.