Musnad Ahmad 1007:120

Hammad ibn Khalid al-Khayyat narrated to us, Malik narrated to us, from Ishaq ibn Abi Talha, from Humaydah, from Kabshah, who said: I saw Abu Qatadah tilt the vessel for a cat, so it drank. He said: "Are you surprised? Indeed, the Prophet, peace and blessings of Allah be upon him, informed us: 'It is not impure; it is among those who go around among you, both males and females.'"