Tafsir: An-Nisa 4:20

The next two verses (20, 21) also enlarge upon this subject. Here it has been said that, should it be that the woman has just not shown any contumacy or immodesty, but the husband, following his own physical desire and pleasure, intends to marry another woman in her place, then again it will not be permissible for him to claim anything from her in exchange of divorce, even though he had given her a lot of wealth. Similarly, it will not be allowed for him to force her to forgo the dower due against him. This is because there is no fault of the woman and the cause which makes the dower due and payable has been vacated, that is, they have been married and have had their privacy with each other. Now, the husband has no right to take back what he has given her or make her forgo the dower.

That the taking back of this amount is an injustice and sin has been later on described in three stages.

First, it was said: أَتَأْخُذُونَهُ بُهْتَانًا وَإِثْمًا مُّبِينًا that is, 'do you want to take it through imputation and an open sin?"

This sentence refers back to the previous verse (19) where it was laid down that the husband has no right to take back the dower from his wife except when she has committed a shameful act. On the basis of this principle the present verse (20) says that if you take back the dower from your wife, it will mean that you are imputing her for a shameful act, because it is the only situation where your claim may be rightful. Since your wife has not committed a shameful act, your claim to the dower is a false imputation which is an open sin.