«القدر مع الجنس في الأموال الربوية»
Measure or quantity together with sameness of kind in usurious commodities.
The book gives this as an ijtihad-derived cause. In the Hanafi analytical framework, the relevant kind of equivalence and measurement or weight may matter when evaluating certain exchanges of ribawi commodities.
The lesson is not a general ruling on all modern financial products. It shows that a cause may be established by disciplined juristic inference from the evidence rather than by a single direct statement. Juristic schools differ in the detailed analysis of the causes of riba.