Musannaf Ibn Abi Shayba 7:269

Yazid ibn Harun narrated to us, he said: Humayd informed us, from Thabit, from Anas, who said: The Messenger of Allah (may Allah bless him and grant him peace) saw a man being supported between his two sons. He said: "What is this?" They said: "He vowed to walk to the House of Allah." He said: "Indeed, Allah is free of need from this one torturing himself." Then he commanded him, so he rode.