"A woman from Khath'am asked the Messenger of Allah . She said: 'O Messenger of Allah, the command of Allah, the Mighty and Sublime, to His slaves to perform Hajj has come while my father is an old man, he cannot sit upright in the saddle. Will it suffice if I perform Hajj on his behalf?' He said: 'Yes.'"
Sunan an-Nasa'i Book 49, Hadith 12