Sahih Muslim Book 007, Hadith Number 2922.
Chapter : It is permissible to observe Tawaf on the back of a camel or any other riding beast, and to touch the black stone with a stick.
Umm Salama reported: I made a complaint to Allah's Messenger (may peace be upon him) of my ailment, whereupon be said: Circumambulate behind the people while riding. She said: So I circumambulated and Allah's Messenger (may peace be upon him) was at that time praying towards the side of the House and he was reciting al-Tur and a Book Inscribed (i.e. Sura lii. of the Qur'an).