What is the ruling on purchasing an apartment in installments from a housing bank with a down payment and a quarterly installment for 15 years, given that its total price exceeds its cash price?

It is permissible to purchase an apartment by paying a portion of the price upfront and the remainder in installments over a known period, with an increase in price for the debt, provided that the bank owns the apartment or purchases it and it transfers to its guarantee.

However, if the reality of the transaction is that the bank lends the buyer the price of the apartment and then charges him the price in installments with an increase, this is impermissible and constitutes forbidden usury (riba), because it involves condoning the usurious bank's transgression and encouraging it. Allah Almighty says: (And cooperate in righteousness and piety, but do not cooperate in sin and aggression).