Is the arrangement of paying a fee to a goldsmith in addition to exchanging metal weight for an item permissible?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
If one asks a goldsmith to fashion a ring of one mithqal weight and offers the equivalent weight in metal plus an extra mithqal as a fee, this arrangement is not considered the sale of one mithqal for two mithqals. The goldsmith is permitted to take both mithqals: one in exchange for the crafted ring and the second as his wage (ujra).