Sayyiduna Jubayr bin Mut'im (may Allah be pleased with him) narrates: In the days of Ignorance I went to Syria for trade. When I drew near to Syria, a man from the People of the Book met me and said: "Is there a prophet among you?" I said: "Yes!" He said: "Would you recognise his picture when you see it?" I said: "Yes!" So he took me into a house where there were various pictures; I did not see the picture of the Prophet (peace and blessings be upon him). While we were there like that, another man from among them came to us and said: "What are you doing?" We told him about it, so he took us to his house. As soon as I entered his house, I saw the picture of the Prophet (peace and blessings be upon him), and there was a man there who was behind the Prophet (peace and blessings be upon him) (or he was holding the heel of the Prophet (peace and blessings be upon him)). I said: "Who is this gentleman standing behind him?" He said: "After every prophet there is a prophet, but after this prophet there will be no prophet; this man is the caliph who will come after him." The narrator says: It was the picture of Sayyiduna Abu Bakr (may Allah be pleased with him).
Al-Tabarani recorded it in al-Mu'jam al-Kabir and al-Mu'jam al-Awsat, and its chain contains narrators whom I do not know.