Is it permissible to sell the bicycle and donate the paid difference, or to keep it and donate the same difference, in order to purify the money from the suspicion of usury and purchasing a stolen item, after being unable to reach the original owner?

It is not forbidden to sell an engine from one motorcycle for an engine from another motorcycle, or spare parts for spare parts, whether a difference in price is paid or not, because these are not usurious commodities. If the sale occurs without the knowledge and permission of the motorcycle owner, the sale is void, and the engine and spare parts must be returned to him, based on the Prophet's (peace be upon him) saying: "If a man's property is stolen, or he loses property and finds it in the possession of a specific person, he has a greater right to it, and the buyer should seek reimbursement of the price from the seller." If it is impossible to reach the owner, the value of these items must be given in charity on his behalf, and the seller should be asked for the price. If he refuses, the matter should be referred to the concerned authorities. It is not permissible to merely give the difference in price as charity or to keep it without returning it to the owner or giving its value in charity on his behalf.