Sahih Bukhari Volume 2, Book 26, Hadith Number 589.
Narated By ‘Abdullah bin Abbas : Al-Fadl (his brother) was riding behind Allah’s Apostle and a woman from the tribe of Khath’am came and Al-Fadl started looking at her and she started looking at him. The Prophet turned Al-Fadl’s face to the other side. The woman said, “O Allah’s Apostle! The obligation of Hajj enjoined by Allah on His devotees has become due on my father and he is old and weak, and he cannot sit firm on the Mount; may I perform Hajj on his behalf?” The Prophet replied, “Yes, you may.” That happened during the Hajj-al-Wida (of the Prophet).