and silk for silk:

The first view is that exchanging a commodity for another of the same kind in unequal amounts is impermissible. This is the position of Abū Hanīfa and his companions, and of Ahmad according to the better-known of the two reports from him.

The second view is that this is permissible. This is the position of Mālik and al-Shāfiʿī, and of Ahmad according to the other report, which a group of his followers adopted.

Those who hold such exchanges to be prohibited disagree about articles manufactured from these materials, such as cotton and linen garments, buckets, copper pots, and other such items. Are they subject to the rules of ribā (usury)? There are three views. The soundest distinguishes between articles whose weight remains a consideration after manufacture—such as silk garments, buckets, and the like—and those whose weight is not a consideration, such as cotton and linen garments, needles, and other such items.

Accordingly, copper coins are subject to the rules of ribā according to those who hold that these rules apply to manufactured copper articles. Those who make customary consideration of weight the criterion do not apply the rules of ribā to copper coins, since their weight is not ordinarily taken into account; rather, they circulate by number.

But among those who regard them as money, do the rules of ribā apply to them on that account? They hold two views on this. Likewise, there are two views on whether zakat is due on them, whether they may be used to pay zakat, and other related matters. Both views are found in the school of Ahmad and elsewhere.