What is the ruling on purchasing an apartment within a social housing project, where the bank pays its value and reclaims it from the buyer with a diminishing interest of 7% annually, along with mortgaging the apartment until the completion of payment?

What is mentioned in the question concerning the bank paying the price of the apartment for the buyer, then collecting it from him in installments with interest, is usury (riba). The bank could have purchased the apartment and sold it to the seeker for a profit, as profit in trade is permissible, whereas profit in a loan is forbidden usury. Allah Almighty said: (But Allah has permitted trade and forbidden interest) and (O you who have believed, fear Allah and give up what remains [due to you] of interest, if you should be believers. And if you do not, then be informed of a war [against you] from Allah and His Messenger. But if you repent, you may have your principal – [thus] you do no wrong, nor are you wronged). The Prophet, peace and blessings of Allah be upon him, cursed the one who consumes usury, the one who feeds it, its scribe, and its two witnesses. Therefore, it is not permissible to enter into this usurious contract.