or gold for gold or silver for silver—this is impermissible by the consensus of the scholars. The same applies to all kinds of food, whether measured by volume or weight or neither, and whether storable or not: none may be advanced in exchange for another.
Section
According to Ibn al-Qāsim’s position, advance-payment sales of manufactured goods fall into four categories: (first) the commissioning buyer neither stipulates that the craftsman he engages must perform the work himself nor specifies the material from which the article is to be made; (second) he stipulates that the craftsman must perform the work himself and specifies the material; (third) he does not stipulate that the craftsman must perform the work himself but specifies the material; and (fourth) he stipulates that the craftsman must perform the work himself but does not specify the material.
The first category, in which neither the craftsman’s personal performance nor the material is specified, is an advance-payment sale governed by the rules of such sales. It is permissible only if the work is described, a delivery date is fixed, and the purchase price is paid in advance.
The second category, in which the craftsman’s personal performance is stipulated and the material is specified, is not an advance-payment sale. Rather, it combines a sale with the hiring of labour to work on the item sold. If the outcome of working on the item is known, or if it is possible to rework it or make another article from the specified material, the transaction is permissible on condition that work begin immediately, or that its commencement be deferred for a stipulated period of up to three days or thereabouts. If work is to begin immediately, either immediate or deferred payment may be stipulated. If work is to begin after a delay of three days or thereabouts, immediate payment may not be stipulated before work begins.
The third category, in which the particular craftsman’s personal performance is not stipulated but the material is specified, likewise combines a sale with the hiring of labour to work on the item sold. Here, however, the work may begin immediately or be deferred for about three days, with payment made either immediately or later.
The fourth category, in which the craftsman’s personal performance is stipulated but the material is not specified, is impermissible in all circumstances, because two conflicting principles apply to it: advance payment is required because the material to be used is guaranteed, yet it is prohibited because the work of the particular craftsman engaged has been stipulated.