Musnad Ahmad 32:946

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 [on foot for Hajj]." He said: "Indeed, Allah is in no need of this person torturing himself." So he commanded him to ride.