Surat An-Nisā' - سورة النساء

وَإِنْ أَرَدتُّمُ اسْتِبْدَالَ زَوْجٍ مَّكَانَ زَوْجٍ وَآتَيْتُمْ إِحْدَاهُنَّ قِنطَارًا فَلَا تَأْخُذُوا مِنْهُ شَيْئًا ۚ أَتَأْخُذُونَهُ بُهْتَانًا وَإِثْمًا مُّبِينًا

Muhsin Khan: But if you intend to replace a wife by another and you have given one of them a Cantar (of gold i.e. a great amount) as Mahr, take not the least bit of it back; would you take it wrongfully without a right and (with) a manifest sin?