Is it valid to sell an animal and stipulate an exception of a known fraction (e.g., one-third) of it?
Chapter on Selling Assets and Fruits
Al-Mughni
Book of Sales
Primary text
It is permissible to sell an animal and stipulate the exception of a known fraction, such as one-third. The ruling is that the sale is valid, and the meaning is that two-thirds of the animal are sold.
Supporting text
Al-Qadi Abu Ya'la prohibited this by analogy with stipulating an exception for fat (shaham). He disallowed it because fat is an unknown entity that cannot be validly isolated for sale on its own. However, the animal's fraction is known and can be validly isolated for sale, just like a specific tree, rendering the analogy based on unknowability invalid.