Is it permissible to purchase a house in installments from a real estate company that sells houses under construction, given that it stipulates the involvement of an insurance company as a third party in the financing process and supervision of construction, with a fixed and predetermined profit margin from the outset, and fixed monthly installments that do not change even in the event of late payment?

Firstly: Selling houses under construction (manufacturing contract) is permissible. If the real estate company owns the land and the financing company participates with money to build the houses, such that the property becomes jointly owned by them, then there is no objection to this partnership, nor to buying from the real estate company and paying the financing company. Installment buying is permissible, even at a higher price, provided the total price is agreed upon.

Secondly: If the role of the financing company is to pay the price to the seller on behalf of the buyer, and then recover the price from the buyer with an increase, this is usury (riba) forbidden by consensus, because it is a loan with an increment. Usurious financing is not inconsistent with the company's supervision of the construction and paying money in installments. It is necessary to verify the nature of the financing company's role in the contract. If the contract is usurious, then it is not permissible to enter into it, even if the buyer did not request the involvement of the financing company, as it involves aiding in usury.