Is the brother entitled to demand that his brother, who bought an apartment from him with a down payment and monthly installments, vacate the apartment without returning what he paid, given that the buyer stopped making payments due to unforeseen circumstances, and knowing that both parties agreed to resort to Sharia law for judgment?

Issues of disputes and litigations are decided by judicial authorities or by agreement between the disputing parties, and a fatwa is not beneficial in such cases. Generally, if a sale is concluded validly and without conditions, ownership of the sold item transfers to the buyer, whether the sale is immediate or in installments. The seller does not have the right to annul the sale due to the buyer's non-payment, except with the buyer's consent. The seller may stipulate in the contract the right to annul it if the buyer fails to pay the full price or a part thereof. In the event of annulment, either by stipulation or mutual consent, the buyer returns the sold item to the seller, and the seller returns the amount received from the price. The seller is not permitted to take anything in exchange for the buyer's use of the sold item, because the buyer owns the sold item and its increments immediately upon the validity of the sale.