Is it permissible for a husband to ask his wife to waive her deferred dower (mu'akhkhar) while their marriage subsists, and is she entitled to retract her waiver in the future?

It is permissible for the husband to request the waiver of the deferred dowry, and the wife's gift is effective if she is an adult, of sound mind, and mature, based on the Almighty's saying: "Unless they [the wives] pardon it," and His saying: "But if they, of their own accord, remit to you anything of it, take it as lawful and pleasant." It is not permissible for her to revoke the gift due to its effectiveness. If the waiver was in exchange for him not divorcing her, then she may revoke her gift if he divorces her soon thereafter. However, if he divorces her after a long time, or dies before divorcing her, she has no right to revoke it according to the Maliki school, though there is another opinion that permits her to revoke it.