Is it permissible to stipulate that the deferred dower (mu'akhkhar) is due only upon divorce, and not upon death, and can this condition be included in the marriage contract?

There is no objection to stipulating the deferral of part of the dowry until divorce, for the Prophet, peace and blessings be upon him, said: "The conditions most worthy of fulfillment are those by which you make intimate relations lawful." If the spouses agree upon a specific amount of money to be paid upon divorce, the husband is obligated to pay it, unless the mature wife waives it. Stipulating that the deferred dowry is due only upon divorce and not upon death is considered a waiver by the wife of her right in the event of death. It must be noted that the mother has no guardianship in marriage; rather, guardianship belongs to the male agnates.