Is purchasing a laptop in installments through an intermediary, where the intermediary adds interest to the remaining amount, considered usury (riba)? And what should the buyer do if that is the case, especially given that he has already paid approximately half of the installments?

Selling an item not currently in the possession of the seller on installment can be done in two ways:

1. Prohibited: The seller pays for the item on behalf of the buyer and then recovers the cost from the buyer in installments with an increase. This constitutes an usurious loan. 2. Permissible (Murabaha sale with its conditions): The seller purchases the item for himself first, then sells it to the buyer after taking possession and holding it.

Conditions for a Permissible Murabaha Sale: 1. The seller must first purchase the item for himself. 2. The seller must take possession of the item and hold it before selling it to the buyer, due to the Prophet's (peace be upon him) prohibition of selling an item before taking possession of it. 3. No down payment should be made to the seller before he owns the item, takes possession of it, and sells it to the buyer, because it is not permissible to combine a loan and a sale. 4. The transaction must be free of any usurious conditions, such as penalties for late payment. 5. Ownership should not be contingent upon the payment of installments, though it is permissible to stipulate a prohibition on selling the item until the installments are paid.

If the purchase was made with a prohibited usurious loan, or if it was made in a seemingly correct manner but a condition was violated and correction is impossible, there is no harm in benefiting from the item while repenting. However, if correction is possible, it is obligatory.