Fiqh-us-Sunnah Volume 1, Purification and Prayer, Fiqh 1.006.

Section : Water left in a pot after a cat has drunk from it.

Such water is also considered pure. This is proven by the hadith of Kabshah bint Ka’b who, when she was under the care of Abu Qatadah, entered the room to pour some water for him. A cat came, drank some of the water, and Qatadah proceeded to tilt the container so the cat could drink more. Kabshah said, “He noticed that I was watching him.” He asked, “Are you surprised, O niece?” I answered, “Yes.” He said, “The Messenger of Allah, upon whom be peace, said, ‘It (the cat) is not impure. They intermingle with you.”‘