It is narrated from Sayyiduna Mu'adh bin Anas al-Juhani (may Allah be pleased with him) that the Messenger of Allah (peace and blessings be upon him) said: "Ride these animals while they are sound, and leave them (to rest) while they are still sound."
Hadith Referenceالمعجم الكبير للطبراني / باب الميم / 17566