Musnad Ahmad 25:512

Ya'qub narrated to us, he said: Ibn Akhi Ibn Shihab narrated to us, from his paternal uncle Muhammad ibn Muslim, he said: Ubayd Allah ibn Abd Allah ibn Utbah ibn Mas'ud informed me, that Abd Allah ibn Abbas informed him: That the Messenger of Allah (peace and blessings of Allah be upon him) wrote to Caesar, inviting him to Islam, and he sent his letter with Dihyah al-Kalbi. The Messenger of Allah (peace and blessings of Allah be upon him) commanded him to deliver it to the Governor of Busra, so that he would deliver it to Caesar. The Governor of Busra delivered it to Caesar. When Allah (Mighty and Majestic is He) removed the armies of Persia from Caesar, he walked from Homs to Iliya (Jerusalem) upon carpets spread out for him. Abd Allah ibn Abbas said: When Caesar received the letter of the Messenger of Allah (peace and blessings of Allah be upon him), he said when he read it: "Seek out for me someone from his people whom I may ask about the Messenger of Allah." Ibn Abbas said: Abu Sufyan ibn Harb informed me that he was in Ash-Sham among men of Quraysh who had come as merchants, and that was during the period of truce between the Messenger of Allah (peace and blessings of Allah be upon him) and the disbelievers of Quraysh. Abu Sufyan said: Caesar’s messenger came to me, and he took me and my companions until we arrived at Iliya. We were brought in to him, and he was sitting in his royal assembly, wearing his crown, and around him were the great men of Rome. He said to his translator: "Ask them, which of them is closest in lineage to this man who claims to be a prophet?" Abu Sufyan said: I am the closest of them to him in lineage. He said: "What is your kinship to him?" I said: He is my cousin. Abu Sufyan said: There was no man from the Banu Abd Manaf in the caravan that day except me. Caesar said: "Bring him near to me." Then he ordered my companions, and they were placed behind my back, near my shoulders. Then he said to his translator: "Tell his companions: I am going to ask this man about this person who claims to be a prophet; if he lies, then call him a liar." Abu Sufyan said: By Allah, were it not for the shame that my companions would report me as a liar, I would have lied about him when he asked me. But I was ashamed that they would report me as a liar, so I spoke the truth about him. Then he said to his translator: "Tell him: How is this man’s 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: "Were you accusing him of lying before he said what he said?" I said: No. He said: "Was there any king among his forefathers?" I said: No. He said: "Do the noble people follow him, or the weak ones?" I said: Rather, the weak ones. He said: "Are they increasing or decreasing?" I said: Rather, they are increasing. He said: "Does anyone apostatize out of hatred for his religion after entering it?" I said: No. He said: "Does he betray?" I said: No, and we are currently in a truce with him, and we fear that. Abu Sufyan said: I was not able to insert any word to disparage him other than that, and I did not fear that it would be reported against me. He said: "Have you fought him, or has he fought you?" I said: Yes. He said: "How was your war and his war?" I said: It was like buckets alternating; we prevail over him one time, and he prevails over us another. He said: "What does he command you?" I said: He commands us to worship Allah alone and not associate anything with Him, and he forbids us from what our fathers used to worship. He commands us to pray, to be truthful, to be chaste, to fulfill promises, and to return trusts. He said to his translator when I told him that: "Tell him: I asked you about his lineage among you, and you claimed that he is of noble lineage among you; and such are the messengers, they are sent in the lineage of their people. I asked you: Has anyone among you ever said this statement before him? And you claimed no. I said: If anyone among you had said this statement before him, I would have said: A man following a statement said before him. I asked you: Were you accusing him of lying before he said what he said? And you claimed no. I know that he would not leave off lying to people and then lie about Allah (Mighty and Majestic is He). I asked you: Was there any king among his forefathers? And you claimed no. I said: If there had been a king among his forefathers, I would have said: A man seeking the kingdom of his forefathers. I asked you: Do the noble people follow him or the weak ones? And you claimed that the weak ones follow him, and they are the followers of the messengers. I asked you: Are they increasing or decreasing? And you claimed that they are increasing; and such is faith until it is complete. I asked you: Does anyone apostatize out of hatred for his religion after entering it? And you claimed no; and such is faith when its joy mixes with the hearts, no one hates it. I asked you: Does he betray? And you claimed no; and such are the messengers. I asked you: Have you fought him and has he fought you? And you claimed that he has, and that your war and his war is alternating; you prevail one time, and you are prevailed upon another; and such are the messengers, they are tested, and the outcome is theirs. I asked you: What does he command you? And you claimed that he commands you to worship Allah (Mighty and Majestic is He) alone, not associating anything with Him, and he forbids you from what your fathers used to worship, and he commands you to be truthful, to pray, to be chaste, to fulfill promises, and to return trusts. This is the description of a prophet whom I knew was going to emerge, but I did not think he would be from among you. If what you said about him is true, then he will soon possess the place of these two feet of mine. By Allah, if I hoped to reach him, I would have endured the hardship of meeting him, and if I were with him, I would have washed his feet." Abu Sufyan said: Then he called for the letter of the Messenger of Allah (peace and blessings of Allah be upon him), and he ordered it to be read. It contained: "In the name of Allah, the Most Gracious, the Most Merciful. From Muhammad, the servant of Allah and His Messenger, to Heraclius, the Great of Rome. Peace be upon whoever follows the guidance. To proceed: I invite you with the invitation of Islam. Submit, and you will be safe; submit, and Allah will give you your reward twice. But if you turn away, then upon you is the sin of the Arisiyyin (meaning the farmers). {Say, "O People of the Scripture, come to a word that is equitable between us and you - that we will not worship except Allah and not associate anything with Him and not take one another as lords instead of Allah." But if they turn away, then say, "Bear witness that we are Muslims."} [Al-Imran: 64]." Abu Sufyan said: When he finished his speech, the voices of those around him from the great men of Rome rose, and their clamor increased, so I do not know what they said. He ordered us to be taken out, and we were taken out. Abu Sufyan said: When I went out with my companions and was alone with them, I said to them: "The affair of Ibn Abi Kabshah has become serious; this King of the Banu al-Asfar fears him." Abu Sufyan said: By Allah, I remained lowly, certain that his affair would prevail, until Allah entered Islam into my heart, while I was reluctant.