Is it obligatory to give in charity the generator bought on credit from a merchant, then sold to another person, if this transaction was usurious, and where would the capital be in this case?

The apparent meaning of the question is that the questioner sold the commodity he had purchased through murabaha to the second merchant by handing over the aforementioned receipt. Receiving the receipt is considered constructive possession of the commodity if it identifies the commodity and enables the buyer to dispose of it. It is permissible to sell it while it is still in the first seller's warehouse, as this is considered valid possession according to some scholars. Thus, possessing documents issued in the name of the possessor or endorsed in their favor is considered constructive possession of what they represent, provided the commodities are identified and the possessor is enabled to dispose of them, such as a bill of lading or warehouse receipts.