He was also asked:

A man said to someone, “Give me half-dirham coins in exchange for these dirhams.” The other replied, “That is not permissible.” Is this permissible?

He answered:

Praise be to Allah. The scholars disagree on this matter, but most permit it, including Abū Hanīfa, Mālik, and Ahmad according to the apparent position of his school. The issue discussed by the jurists as the case of “a mudd of ʿajwa dates” falls into three categories. What they have in common is the exchange of a commodity subject to the rules of ribā for another of the same kind, with something of a different kind accompanying either or both.

The first category:

The intention is to exchange a commodity subject to the rules of ribā for an unequal amount of the same kind, adding something of a different kind to the smaller amount as a legal stratagem. Examples include exchanging two thousand dinars for one thousand dinars wrapped in a cloth, or a measure (qafīz) of wheat for an equal measure plus a sack, and similar transactions. The correct view is that such transactions are prohibited, as held by Mālik, al-Shāfiʿī, and Ahmad. Otherwise, anyone engaging in ribā through unequal exchange could simply add something of this sort to the smaller amount.

The second category:

The intention is to sell an item not subject to the rules of ribā together with an item that is, the latter being included only incidentally and as an accessory. An example is selling a ewe bearing wool and producing milk for another ewe with