Sayyiduna Abdullah bin Abbas (may Allah be pleased with them both) says: A woman from the tribe of Khath'am said to the Messenger of Allah (peace and blessings be upon him) during the Farewell Pilgrimage, while Fadl (may Allah be pleased with him) was riding behind him: The divine obligation of Hajj has reached my father in old age, such that he cannot remain seated on a mount; will my performing Hajj on his behalf suffice? He (peace and blessings be upon him) said to her: "Yes."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8630