The Quran

وَإِن أَرَدتُمُ استِبدالَ زَوجٍ مَكانَ زَوجٍ وَآتَيتُم إِحداهُنَّ قِنطارًا فَلا تَأخُذوا مِنهُ شَيئًا ۚ أَتَأخُذونَهُ بُهتانًا وَإِثمًا مُبينًا

Muhammad Asad

But if you desire to give up a wife and to take another in her stead, do not take away anything of what you have given the first one, however much it may have been.¹ Would you, perchance, take it away by slandering her and thus committing a manifest sin?²

Lit., "if you desire the exchange of a wife in place of a wife, and you have given one of them a treasure (qintar), do not take away anything thereof". The allusion to the "exchange" of one wife for another is a clear indication of the Qur'anic view that a monogamous marriage is the desirable norm.
I.e., by falsely accusing her of immoral conduct in the hope of regaining her dower (see note on verse 19 above).