His statement, “provided that neither of them is currency”: he did not say, “provided that neither of them is gold or silver,” because if one of them is gold or silver, the two parties must take possession in the contract session. Thus, if I sell you one dirham for one dinar, possession must take place in the contract session, as established by the many hadiths from the Prophet, peace and blessings be upon him. Likewise, if I sell you gold jewelry in exchange for some copper, possession must take place, because the author says, “provided that neither of them is currency,” rather than saying, “gold or silver.”

“Such as two commodities sold by measure or two commodities sold by weight; and if they part before taking possession, the sale is invalid.”

His statement, “such as two commodities sold by measure,” means when one is sold in exchange for the other.

His statement, “and two commodities sold by weight,” likewise means when one is sold in exchange for the other. In both cases, deferment is prohibited.

The evidence for this is the Prophet’s saying: “When these categories differ, then sell as you wish, provided it is hand to hand.” (1) He made taking possession obligatory, and making possession obligatory entails the prohibition of deferment.

Examples:

If he sells barley for wheat, deferment is not permissible, because they share the effective cause of excess usury, namely measurement by volume.

If he sells wheat for iron, deferment is permissible, because they differ with respect to the effective cause of excess usury.

If he sells one ton of lead for one ton of copper, it is not permissible, because they share the effective cause of excess usury, namely weight.