Musnad Ahmad 1889

It was narrated from Ibn "Abbas that a woman of Khath’am asked the Messenger of Allah (ﷺ) on the morning of Muzdalifah, when al-Fadl bin ‘Abbas was seated behind him on his mount: Allah has made Hajj obligatory for His slaves when my father is an old man and cannot stay on his mount; do you think that I can do Hajj on his behalf? He said: "Yes."