حكمه: لا يعمل به إلا بعد بيان المتكلم المجمل.
Its ruling is that the ambiguous expression is acted upon only after clarification from the speaker who made it.
This does not mean every independently clear ruling is suspended. It concerns the particular aspect that remains undetermined and needs authoritative specification before its application.
In the riba illustration, the basic prohibition stands. The technical judgment about whether a particular transaction is riba must be established through valid scriptural and juristic evidence. An unsupported personal guess cannot replace the authoritative clarification required for mujmal.