Musnad Ahmad

It is narrated from Hazrat Abu Bakr Siddiq (may Allah be pleased with him) that when the Prophet (peace and blessings be upon him) sent him as the leader of Hajj, he also entrusted him with the responsibility of announcing to the people of Makkah this declaration of disassociation: that after this year, no polytheist will be able to perform Hajj, no man will be able to circumambulate the Ka'bah naked, only that person will enter Paradise who is a Muslim, and if anyone has a treaty with the Prophet of Islam (peace and blessings be upon him) for a specific period, it will remain valid until its term ends, and that Allah and His Messenger are free from (obligations to) the polytheists. When Hazrat Abu Bakr Siddiq (may Allah be pleased with him) set out with this message and had covered a distance of three days, the Prophet (peace and blessings be upon him) said to Hazrat Ali (may Allah be pleased with him): "Go after Abu Bakr, call him back to me, and you are not to lead the Hajj, but only to deliver the message to the people of Makkah." Hazrat Ali (may Allah be pleased with him) set out. When Hazrat Abu Bakr Siddiq (may Allah be pleased with him) returned, tears were flowing from his eyes and he said, "O Messenger of Allah! Has something new happened regarding me?" The Prophet (peace and blessings be upon him) said: "Only good can happen regarding you. The real matter is that, according to the custom of the Arabs, either I myself could deliver this message to the people of Makkah, or a member of my family. That is why I have entrusted this responsibility only to Ali."