Is mortgaging (Pledging) forbidden or permissible, and if permissible, what are its conditions?

If the questioner means 'wagering' by al-rahan, then the answer to his question is in Fatwa no. 46693. But if he means al-rahan in its Shar'i sense, which is money given as collateral for a debt, then Fatwa no. 67412 should be consulted regarding it.