Maliks Muwatta Book 21, Hadith Number 47.

Section : Horses and Racing Them and Expending in Military Expeditions.

Yahya related to me from Malik from Yahya ibn Said that the Messenger of Allah, may Allah bless him and grant him peace, was seen wiping the face of his horse with his cloak. He was questioned about it and said, “I was reproached in the night about horses.” i.e. not taking care of them.