Musnad Ahmad 32:187

Yahya narrated to us, from Humayd, from Thabit, from Anas, that the Messenger of Allah (peace and blessings of Allah be upon him) passed by a man who was being supported between his two sons. They said: "He vowed to walk." He said: "Indeed, Allah is in no need of this man torturing himself." So he commanded him to ride.