How should the “claim accompanied by evidence” comparison be understood?

Taʿrīḍ, Talwīḥ, Ramz, Īmāʾ and Ishārah; the Rhetorical Force of Figurative Speech

As a statutory standard of legal testimony
As proof that all ash implies generosity
As proof that literal wording is prohibited
As rhetorical supporting indication, not invariably conclusive proof