«حكمه: المقيد يجري على تقييده»
Its ruling is that a restricted expression is applied according to its restriction.
When the expiation for accidental killing specifies mu’minah, the adjective cannot be silently dropped. Fulfilment requires attention to the noun and its qualification.
Similarly, if an instruction is “Bring an Arabic book,” a non-Arabic book does not fulfil it just because it is a book: the required language is part of the instruction.