It was the practice of the Prophet (peace and blessings be upon him):
"He (peace and blessings be upon him) would tilt the vessel for a cat so that it could drink from it, and then he would perform ablution with the water it had left."
Hadith Referenceصحیح الجامع الصغیر / حرف الكاف / 4958
Hadith Gradingالألبانی:صحيح
Hadith Takhrij[طس حل] عن عائشة. صحيح أبي داود ٦٩: د، هـ، الطحاوي، قط، هق.