فالعلة فيه الكيل مع الجنس أو الوزن مع الجنس
Translation: Its legal cause is volumetric measurement together with sameness of genus, or weight together with sameness of genus.
Two attributes are checked:
Sameness of genus: both countervalues belong to one genus, such as wheat for wheat.
Sameness of governing measure: both fall under the same recognized modality, volume or weight.
Both attributes together prohibit inequality and deferred exchange. If only one is present, inequality may be permitted but delay remains prohibited. This is the classical Hanafi analysis; other Sunni schools formulate the legal causes differently.