Surah An-Nisa Verse 20 - English Translation by N J Dawood
Surah An-Nisaوَإِنۡ أَرَدتُّمُ ٱسۡتِبۡدَالَ زَوۡجٖ مَّكَانَ زَوۡجٖ وَءَاتَيۡتُمۡ إِحۡدَىٰهُنَّ قِنطَارٗا فَلَا تَأۡخُذُواْ مِنۡهُ شَيۡـًٔاۚ أَتَأۡخُذُونَهُۥ بُهۡتَٰنٗا وَإِثۡمٗا مُّبِينٗا
If you wish to replace one wife with another, do not take anything from the dowry you gave her even if it be a talent. That would be improper and a veritable sin