Is it permissible for a wife, who has been given a house and a car as a trust, to dispose of them by selling one of the houses and the car without the permission of the grantor, and is her action considered a betrayal of trust?

If the gift is a sham, meaning that the donor and the donee did not truly intend the contract, it is void according to the Hanafis and Hanbalis. This is known as a sale of compulsion (bay' al-talji'ah) or a sham gift. The jurists have based this on the hadith: "There are three things which, whether done seriously or in jest, are considered serious: marriage, divorce, and revocation [of divorce]." They point out that one who jokes about a contract is bound by its ruling. Consequently, a sham gift is not valid, and the effects of a gift do not result from it. And if the wife disposes of the gifted item without the donor's permission, knowing that it is a sham gift or a trust (wadi'ah), then this is considered a betrayal of trust.