Surah An-Nisa' (The Women), Verse 20

وَاِنْ اَرَدْتُّمُ اسْتِبْدَالَ زَوْجٍ مَّكَانَ زَوْجٍ وَّاٰتَیْتُمْ اِحْدٰىهُنَّ قِنْطَارًا فَلَا تَاْخُذُوْا مِنْهُ شَیْـًٔا اَتَاْخُذُوْنَهٗ بُهْتَانًا وَّاِثْمًا مُّبِیْنًا ۟

Wa in arattumustib daala zawjim makaana zawjin wa aataitum ihdaahunna qintaaran falaa ta'khuzoo minhu shai'aa; ata'khuzoonahoo buhtaannanw wa ismam mubeenaa

“But if ye decide to take one wife in place of another, even if ye had given the latter a whole treasure for dower, Take not the least bit of it back: Would ye take it by slander and manifest wrong?”

Quran 4:20 (Yusuf Ali Translation)