الهرة ليست بنجسة، فإنها من الطوافين عليكم والطوافات
The cat is not impure, for it is among those that move frequently among you.
The statement supplies both a ruling and an accompanying rationale. Suʾr means water left in a vessel after an animal drinks from it.
Two inquiries must be separated: determine the cat's original ruling, then investigate whether another animal shares the legally relevant cause. Living in the same house alone does not settle every associated rule.