It was narrated from Ibn 'Abbas that his brother Fadl was riding behind the Messenger of Allah in the morning of the day of sacrifice (i.e., the 10the of Dhul-Hijjah), when a woman from Khath'am came and said: "0 Messenger of Allah, the command of Allah has come for His slaves to perform Hajj, but my father is
an old man and cannot ride. May I perform Hajj on his behalf?" He said: "Yes, because if your father owed a debt you would pay it off." (Sahih)