Musnad Abu Ya'la al-Mawsili 111:5

Ibn Abbas said: Abu Sufyan ibn Harb informed me that they were in Ash-Sham as merchants, and that was during the period that was between the Messenger of Allah (may Allah bless him and grant him peace) and the disbelievers of Quraysh. Abu Sufyan said: The messenger of Caesar came to us, and he took me and my companions until we arrived at Iliya (Jerusalem). He brought us in to him, and he was sitting in his royal assembly wearing the crown, and the notables of Rome were with him. He said to his translator: "Ask them: which of them is the closest in lineage to this man who claims that he is a prophet?" Abu Sufyan said: I said, "I am the closest of them to him." He said, "What is your kinship to him?" I said, "He is my cousin." And there was not a man from the Banu Abd Manaf in the caravan that day except for me. He said, so Caesar said, "Bring him near to me." He ordered my companions, and they were placed behind my back. Then he said to his translator, "I am going to ask this man about this person who claims that he is a prophet; if he lies, then call him a liar." Abu Sufyan said: Were it not for the shame that day that my companions would report a lie about me, I would have lied when he asked, but I was ashamed that they would report a lie about me, so I spoke the truth about him. Then he said to his translator, "Ask: How is his lineage among you?" I said, "He is of noble lineage among us." He said, "Has anyone among you ever said this statement before him?" I said, "No." He said, "Did you accuse him of lying before he said what he said?" I said, "No." He said, "Was there a king among his forefathers?" I said, "No." He said, "Do the nobles of the people follow him, or their weak ones?" I said, "Rather, their weak ones." He said, "Are they increasing or decreasing?" I said, "Rather, they are increasing." He said, "Does he betray?" I said, "No, and we are now in a period of truce with him, and we fear that." Abu Sufyan said: I was not able to insert a word into it to disparage him, because I feared that something else would be reported about me. He said, "Have you fought him?" I said, "Yes." He said, "How was your war and his war?" I said, "It was alternating; he would prevail over us one time, and we would prevail over him another." He said, "What does he command you?" I said, "He commands us to worship Allah and not associate anything with Him, and he forbids us from what our forefathers used to worship, and he commands us to pray, to give charity, to fulfill covenants, and to discharge trusts." He said, so he said to his translator when I said that: "I asked you about his lineage among you, and you claimed that he is of noble lineage among you; and likewise, messengers are sent from the lineages of their people. I asked you if anyone among you had said this statement before him, and you claimed that they had not; so I said, if anyone among them had said this statement before him, I would have said a man following a statement that was said before him. I asked you if you accused him of lying before he said what he said, and you claimed that you did not; so I said, he would not leave off lying to people and then lie about Allah. I asked you if there was a king among his forefathers, and you claimed that there was not; so I said, if there was a king among his forefathers, I would have said a man seeking the kingdom of his father. I asked you if the nobles of the people follow him or their weak ones, and you claimed that their weak ones follow him, and they are the followers of the messengers." And he asked you... and he mentioned the rest of the hadith.