Sunan An-Nasa'i

It was narrated from Al-Fadl bin 'Abbas that:he was riding behind the Messenger of Allah and a man came and said: ""O Messenger of Allah! My mother is an old woman and she cannot sit firmly in the saddle. If I tie her I fear that I may kill her."" The Messenger of Allah said: ""Don't you think that if your mother owed a debt you would pay it off?"" He said: ""Yes."" Her said: ""Then perform Hajj on behalf of your mother.""(Shih)