What is the ruling on selling an apartment through real estate financing, bearing in mind that the contract is tripartite and states that the buyer pays a portion and the bank finances the rest with an 8% interest rate, and in this case, is the seller of the apartment sinful for usury, or considered a witness to it, or a usurer?

Real estate financing in the aforementioned format is a usurious, forbidden contract. If the seller attends the usurious contract between the bank and the buyer, then he is thereby assisting in sin, for Allah Almighty says: "And do not cooperate in sin and aggression." The Messenger of Allah, peace and blessings be upon him, cursed the one who consumes usury, the one who feeds it, its scribe, and its two witnesses, and he said: "They are all equal," because the act of the scribe and the witness involves assisting in the sin of usury, and because they consented to it and aided in it, and aiding in disobedience makes its doer sinful.