What is the ruling on exchanging a type of low-grade date vinegar (khal al-daql) with itself?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
It is permissible to exchange a portion of date vinegar for an equal portion of itself. This is because the water content in each portion is unintentional and serves the benefit of the vinegar, thus not preventing the exchange's validity, similar to bread for bread or dates with pits exchanged for dates with pits. However, one type cannot be exchanged for another type.
Supporting text
The exchange between different types is forbidden because the foreign substance (water/impurities) varies in quantity, leading to unequal exchange.