Is the sale of gold or silver coins permissible when they differ in quality (good/bad) or form (ingot/minted, whole/broken) with the condition of equal exchange by weight?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
The sale of gold or silver when identical in weight, regardless of differences in quality (good or bad), form (ingot or struck), or condition (whole or broken), is permissible. This is the position held by the majority of scholars, including Abu Hanifa and Al-Shafi'i. The evidence for this ruling is the Prophet's saying: 'Gold for gold, like for like, and silver for silver, like for like.' Furthermore, it is narrated from Ubadah that the Prophet peace be upon him said: 'Gold for gold, its ingot and its minted form, and silver for silver, its ingot and its minted form.' The comparison is established because they are equal in weight, and thus, differences in value do not affect the permissibility of exchange, just as with good and bad quality items.
Supporting text
A narration attributed to Malik suggests that the sale of struck coins for their equivalent weight in ingots of the same metal is permissible, although his companions rejected this view. A narration mentioned from Ahmad suggests that selling whole coins for broken ones is not permissible because the craftsmanship carries value, effectively adding a value to the metal itself.