Is it Islamically permissible to annul the sale of a mortgaged house for which the buyer has not paid its installments, and what is the ruling on selling a mortgaged item while the mortgage remains in effect, and is the sale in such a form originally permissible?

The legal ruling regarding the sale of a house mortgaged to the Real Estate Development Fund is summarized as follows: If the condition stipulated that the sale is not permissible during the mortgage period, then the sale is invalid. In this case, the money must be returned to the buyer, and the rent for the house must be reclaimed from him. However, if the Fund's conditions permit the sale, then the sale is valid and cannot be revoked except by mutual consent, and there is no right to demand rent for the house. There is no element of deception (ghabn) in this sale, and it is unlawful for the buyer to delay payment of the remaining price if he is wealthy and able to do so.