Is it permissible to sell milk adulterated with water or other substances?
Chapter on Riba (Usury) and Exchange (Sarf)
Al-Mughni
Book of Sales
Primary text
If one type of milk is mixed with water or another substance, it is impermissible to sell it for pure milk of the same species, or for mixed milk of the same species. This prohibition is based on the presence of a non-milk substance introduced without a valid legal justification (maslaha).