I have donated a portion of gold to Allah; is it permissible to give its value without selling it?

If the gifted gold has been taken possession of, then it is not permissible to revoke the gift. However, if it has not been taken possession of, and the donor's intention was charity (sadaqa), then it is permissible to keep the gold and give its price in charity, because revoking a charity is permissible as long as the poor person has not taken possession of it, and it is permissible to change the intention of the charity before it is given.