Is a wife's renunciation or gift of her Mahr (dower) to her husband valid?

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It is valid and legally binding for a wife, who has full authority over her wealth, to waive, forgive, or gift all or part of the Mahr owed to her by her husband after she has already taken possession of it. This ruling is unanimously accepted, with no known difference of opinion. The evidence for this is the saying of Allah the Almighty: "Except that they forego (it) or forgo that in whose hands is the marriage contract" (Quran 2:237), referring to the wives. Furthermore, Allah states: "But if they willingly give up to you anything of it, then consume it in lawful and pleasant fashion" (Quran 4:4). Imam Ahmad, according to the narration of Al-Marwadhi, held that this verse applies to everything, stating that Allah called it "lawful and pleasant" (hanian mariyan), thereby including what the wife gifts to the husband from her Mahr. Alqamah is also reported to have said to his wife, "Gift me from the 'hanian mariyan,'" meaning from her Mahr.