Is it obligatory to return gold or money to a former fiancé who withdrew from the engagement, especially after the price of gold has doubled, and with knowledge of the reasons for his withdrawal and after the fiancée has gotten married?

If a man explicitly states that he has left you gold after breaking off the engagement, then he is not entitled to take it back, whether it was a gift or a release from a debt. It is not permissible to revoke a gift, based on the Prophet’s (peace be upon him) saying: “It is not lawful for anyone to give a gift and then take it back, except for a father in what he gives to his child,” and his saying: “The one who takes back his gift is like a dog that vomits and then returns to its vomit.” As for revoking a release from a debt after its acceptance, it is impermissible by consensus, because it is an annulment, and what has been annulled does not return.