What is the ruling of Islamic law concerning "Ar-Rahn" (pledging/mortgaging) as practiced in Morocco, which involves the tenant paying a sum of money (an advance/loan) to the landlord in exchange for reducing the rent by half or by a third, with a loan agreement written between the two parties?

The described scenario, where one person (Al-Mukhtar) lends a sum of money to another (Ammar), and Ammar then rents his house to Al-Mukhtar at a lower-than-usual rent in exchange for the loan, is not permissible. This is because it involves the lender benefiting from his loan, which is forbidden and considered a form of usury (riba). This is not akin to a permissible mortgage (rahn), which does not allow the mortgagee to benefit from the mortgaged item in exchange for the loan.