How can the wife take possession of the money that her husband deposited in her bank account, saying: "If I die, the money is yours," so that it becomes her property?

A gift contingent upon the death of the donor is considered a bequest (وصية). A bequest to an heir is not valid unless approved by the other heirs. For a gift to be valid, it must be immediate (منجزة), not contingent upon death, and it must be taken possession of by the wife. Possession is a condition for the completion and binding nature of a gift according to the majority of jurists. Possession is achieved by enabling the donee to dispose of the property, and this includes constructive possession, such as a bank entry or the receipt of a check.