Musnad Ahmad 5:33

Sufyan narrated to us, from Abu Ishaq, from Zayd ibn Athi', a man from Hamdan, who said: We asked Ali, "For what were you sent?"—meaning the day the Prophet, peace and blessings of Allah be upon him, sent him with Abu Bakr during the Hajj. He said: "I was sent with four things: No soul shall enter Paradise except a believing soul; no one shall circumambulate the House while naked; whoever has a treaty between himself and the Prophet, peace and blessings of Allah be upon him, then his treaty is until its term; and the polytheists shall not perform Hajj after this year of theirs."