Sunan Ibn Majah Book 1, Hadith 101

She poured water for Abu Qatadah to perform ablution. A cat came and drank the water, and he tilted the vessel for it. She started looking at it (in surprise) and he said: "O daughter of my brother, do you find it strange? The Messenger of Allah said: 'They (cats) are not impure, they are of those who go around among you.'"

Previous Hadith

"The Messenger of Allah said: 'If a dog licks the vessel of anyone of you, let him wash it seven times.'"

Sunan Ibn Majah Book 1, Hadith 100
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"The Messenger of Allah and I used to perform ablution from a single vessel, when the cat had drunk from it beforehand."

Sunan Ibn Majah Book 1, Hadith 102