Is an agreement to supply sesame that the seller does not own at the time of the contract considered selling what one does not own, or is it like selling a fungible item by description, such as in a forward contract (salaf)?

If the commodity agreed upon for sale is specified by a description that removes ambiguity, along with knowledge of its type, quantity, and kind, and the delivery time is such that the existence of the muslam fīh (commodity) at the muslam ilayh (seller) is highly probable, typically at harvest time, and the capital was handed over to the muslam ilayh at the contracting session, then it is a permissible salām sale according to Islamic law. However, if the contract fulfills all conditions of a salām sale except for the receipt of the price at the contracting session, then it is not a salām sale. Rather, it is merely a promise to buy and sell, which is permissible provided that either or both parties have the option [to renege]. Enforcing the promise is not valid unless the seller owns the commodity, so that it does not become a sale of what one does not possess.