Imam Ja'far al-Sadiq, may Allah have mercy on him, narrates from his father (Imam Muhammad al-Baqir, may Allah have mercy on him): It was asked from Sayyiduna Ali, may Allah be pleased with him (or perhaps Imam Zayn al-Abidin, may Allah have mercy on him), about the leftover water of a cat. He replied: "It is included among the beasts, and there is no harm in it (i.e., in its leftover water)."
Hadith Referenceسنن الدارقطني / كتاب الطهارة / 220
Hadith Takhrij«أخرجه الدارقطني فى ((سننه)) برقم: 220، وأورده ابن حجر فى "المطالب العالية"، 20، وأخرجه ابن أبى شيبة فى ((مصنفه)) برقم: 338»