Musnad Ahmad 132:31

Hajjaj narrated to us, Layth ibn Sa'd informed us, he said: Yazid ibn Abi Habib narrated to me, from Ibn Mu'adh ibn Anas, from his father, and he was one of the companions of the Messenger of Allah (may Allah bless him and grant him peace), that he mentioned: That the Messenger of Allah (may Allah bless him and grant him peace) said: "Ride these animals while they are healthy, and leave them (or let them go) while they are healthy, and do not take them as chairs."