It is narrated from Sayyiduna Abu Hurayrah (may Allah be pleased with him) that he (peace and blessings be upon him) said: "When a dog puts its mouth into a vessel, its purification is that you wash it seven times, and the first time with dust." Then Abu Hurayrah (may Allah be pleased with him) made mention of the cat; I do not know whether he said once or twice.
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الطهارة / 1169