He was riding behind the Messenger of Allah , when a man came and said: "O Messenger of Allah, my mother is an old woman; if I put her on a mount she cannot sit firmly, and if I tie her, I fear that I may kill her." He said: "Do you think that if your mother owed a debt you would pay it off for her?" He said: "Yes." He said: "Then perform Hajj on behalf of your mother."
Sunan an-Nasa'i Book 49, Hadith 16