Is it permissible for a woman to forgo the deferred dower (mu'akhkhar al-sadaq) on condition that her husband acknowledges it in front of her father, and does this deferred dower become void if she later demands it?

If the wife tells the suitor: "Accept the deferred dowry stipulated by the guardian, and I forgive it; I do not want it," then this is considered a promise of a gift, and fulfilling a promise is obligatory according to some scholars. If the wife confirms the waiver after the marriage contract, her waiver is valid, and she cannot retract or demand it, because retraction from absolution is forbidden, as stated in the Almighty's saying: "And give women their dowries as a free gift; but if they, of their own good pleasure, remit any part of it to you, take it and enjoy it with good cheer." (An-Nisa/4), and like the prohibition of retracting a gift, as the Prophet (peace be upon him) said: "The one who retracts his gift is like a dog that vomits and then returns to its vomit." Absolving a debt is valid even if it is before its due date and does not require acceptance.