Narrated Ibn `Abbas:

Abu Sufyan narrated to me personally, saying, "I set out during the Truce that had been concluded between me and Allah's Messenger. While I was in Sham, a letter sent by the Prophet (ﷺ) was brought to Heraclius. Dihya Al-Kalbi had brought and given it to the governor of Busra, and the latter forwarded it to Heraclius. Heraclius said, 'Is there anyone from the people of this man who claims to be a prophet?' The people replied, 'Yes.' So I along with some of Quraishi men were called and we entered upon Heraclius, and we were seated in front of him. Then he said, 'Who amongst you is the nearest relative to the man who claims to be a prophet?' So they made me sit in front of him and made my companions sit behind me. Then he called upon his translator and said (to him). 'Tell them ( i.e. Abu Sufyan's companions) that I am going to ask him (i.e. Abu Sufyan) regarding that man who claims to be a prophet. So, if he tell me a lie, they should contradict him (instantly).' By Allah, had I not been afraid that my companions would consider me a liar, I would have told lies. Heraclius then said to his translator, 'Ask him: What is his (i.e. the Prophet's) family status amongst you? I said, 'He belongs to a noble family amongst us." Heraclius said, 'Was any of his ancestors a king?' I said, 'No.' He said, 'Did you ever accuse him of telling lies before his saying what he has said?' I said, 'No.' He said, 'Do the nobles follow him or the poor people?' I said, 'It is the poor who followed him.' He said, 'Is the number of his follower increasing or decreasing?' I said, 'The are increasing.' He said, 'Does anyone renounce his religion (i.e. Islam) after embracing it, being displeased with it?' I said, 'No.' He said, 'Did you fight with him?' I replied, 'Yes.' He said, 'How was your fighting with him?' I said, 'The fighting between us was undecided and victory was shared by him and us by turns. He inflicts casualties upon us and we inflict casualties upon him.' He said, 'Did he ever betray?' I said, 'No, but now we are away from him in this truce and we do not know what he will do in it" Abu Sufyan added, "By Allah, I was not able to insert in my speech a word (against him) except that. Heraclius said, 'Did anybody else (amongst you) ever claimed the same (i.e. Islam) before him? I said, 'No.' Then Heraclius told his translator to tell me (i.e. Abu Sufyan), 'I asked you about his family status amongst you, and you told me that he comes from a noble family amongst you Verily, all Apostles come from the noblest family among their people. Then I asked you whether any of his ancestors was a king, and you denied that. Thereupon I thought that had one of his fore-fathers been a king, I would have said that he (i.e. Muhammad) was seeking to rule the kingdom of his fore-fathers. Then I asked you regarding his followers, whether they were the noble or the poor among the people, and you said that they were only the poor (who follow him). In fact, such are the followers of the Apostles. Then I asked you whether you have ever accused him of telling lies before saying what he said, and your reply was in the negative. Therefore, I took for granted that a man who did not tell a lie about others, could ever tell a lie about Allah. Then I asked you whether anyone of his followers had renounced his religion (i.e. Islam) after embracing it, being displeased with it, and you denied that. And such is Faith when it mixes with the cheerfulness of the hearts. Then I asked you whether his followers were increasing or decreasing. You claimed that they were increasing. That is the way of true faith till it is complete. Then I asked you whether you had ever fought with him, and you claimed that you had fought with him and the battle between you and him was undecided and the victory was shared by you and him in turns; he inflicted casual ties upon you and you inflicted casualties upon them. Such is the case with the Apostles; they are out to test and the final victory is for them. Then I asked you whether he had ever betrayed; you claimed that he had never betrayed. I need, Apostles never betray. Then I asked you whether anyone had said this statement before him; and you denied that. Thereupon I thought if somebody had said that statement before him, then I would have said that he was but a man copying some sayings said before him." Abu Safyan said, "Heraclius then asked me, 'What does he order you to do?' I said, 'He orders us (to offer) prayers and (to pay) Zakat and to keep good relationship with the Kith and kin and to be chaste.' Then Heraclius said, 'If whatever you have said, is true, he is really a prophet, and I knew that he ( i.e. the Prophet (ﷺ) ) was going to appear, but I never thought that he would be from amongst you. If I were certain that I can reach him, I would like to meet him and if I were with him, I would wash his feet; and his kingdom will expand (surely to what is under my feet.' Then Heraclius asked for the letter of Allah's Messenger (ﷺ) and read it wherein was written: "In the Name of Allah, the Most Beneficent, the Most Merciful. This letter is) from Muhammad, Apostle of Allah, to Heraclius, the sovereign of Byzantine........ Peace be upon him who follows the Right Path. Now then, I call you to embrace Islam. Embrace Islam and you will be saved (from Allah's Punishment); embrace Islam, and Allah will give you a double reward, but if you reject this, you will be responsible for the sins of the tillers (i.e. the people of your kingdom) and (Allah's Statement):--"O the people of the Scripture (Jews and Christians)! Come to a word common to you and us that we worship None but Allah....bear witness that we are Muslims.' (3.64) When he finished reading the letter, voices grew louder near him and there was a great hue and cry, and we were ordered to go out." Abu Sufyan added, "While coming out, I said to my companions, 'The situation of Ibn Abu Kabsha (i.e. Muhammad) has become strong; even the king of Banu Al14 Asfar is afraid of him.' So I continued to believe that Allah's Messenger (ﷺ) would be victorious, till Allah made me embrace Islam." Az-Zuhri said, "Heraclius then invited all the chiefs of the Byzantines and had them assembled in his house and said, 'O group of Byzantines! Do you wish to have a permanent success and guidance and that your kingdom should remain with you?' (Immediately after hearing that), they rushed towards the gate like onagers, but they found them closed. Heraclius then said, 'Bring them back to me.' So he called them and said, 'I just wanted to test the strength of your adherence to your religion. Now I have observed of you that which I like.' Then the people fell in prostration before him and became pleased with him." (See Hadith No. 6,Vol 1)

Narrated `Abdullah bin `Abbas:

Allah's Messenger (ﷺ) wrote to Caesar and invited him to Islam and sent him his letter with Dihya Al-Kalbi whom Allah's Messenger (ﷺ) ordered to hand it over to the Governor of Busra who would forward it to Caesar. Caesar as a sign of gratitude to Allah, had walked from Hims to Ilya (i.e. Jerusalem) when Allah had granted Him victory over the Persian forces. So, when the letter of Allah's Messenger (ﷺ) reached Caesar, he said after reading it, 'Seek for me any one of his people! (Arabs of Quraish tribe) if present here, in order to ask him about Allah's Messenger. At that time Abu Sufyan bin Harb was in Sham with some men from Quraish who had come (to Sham) as merchants during the truce that had been concluded between Allah's Messenger; and the infidels of Quraish. Abu Sufyan said, Caesar's messenger found us somewhere in Sham so he took me and my companions to Ilya and we were admitted into Ceasar's court to find him sitting in his royal court wearing a crown and surrounded by the senior dignitaries of the Byzantine. He said to his translator. 'Ask them who amongst them is a close relation to the man who claims to be a prophet." Abu Sufyan added, "I replied, 'I am the nearest relative to him.' He asked, 'What degree of relationship do you have with him?' I replied, 'He is my cousin,' and there was none of Bani Abu Manaf in the caravan except myself. Caesar said, 'Let him come nearer.' He then ordered that my companions stand behind me near my shoulder and said to his translator, 'Tell his companions that I am going to ask this man about the man who claims to be a prophet. If he tells a lie, they should contradict him immediately." Abu Sufyan added, "By Allah! Had it not been shameful that my companions label me a liar, I would not have spoken the truth about him when he asked me. But I considered it shameful to be called a liar by my companions. So I told the truth. He then said to his translator, 'Ask him what kind of family does he belong to.' I replied, 'He belongs to a noble family amongst us.' He said, 'Have anybody else amongst you ever claimed the same before him? 'I replied, 'No.' He said, 'Had you ever blamed him for telling lies before he claimed what he claimed? ' I replied, 'No.' He said, 'Was anybody amongst his ancestors a king?' I replied, 'No.' He said, "Do the noble or the poor follow him?' I replied, 'It is the poor who follow him.' He said, 'Are they increasing or decreasing (day by day)?' I replied,' They are increasing.' He said, 'Does anybody amongst those who embrace his (the Prophet's) Religion become displeased and then discard his Religion?'. I replied, 'No. ' He said, 'Does he break his promises? I replied, 'No, but we are now at truce with him and we are afraid that he may betray us." Abu Sufyan added, "Other than the last sentence, I could not say anything against him. Caesar then asked, 'Have you ever had a war with him?' I replied, 'Yes.' He said, 'What was the outcome of your battles with him?' I replied, 'The result was unstable; sometimes he was victorious and sometimes we.' He said, 'What does he order you to do?' I said, 'He tells us to worship Allah alone, and not to worship others along with Him, and to leave all that our fore-fathers used to worship. He orders us to pray, give in charity, be chaste, keep promises and return what is entrusted to us.' When I had said that, Caesar said to his translator, 'Say to him: I ask you about his lineage and your reply was that he belonged to a noble family. In fact, all the apostles came from the noblest lineage of their nations. Then I questioned you whether anybody else amongst you had claimed such a thing, and your reply was in the negative. If the answer had been in the affirmative, I would have thought that this man was following a claim that had been said before him. When I asked you whether he was ever blamed for telling lies, your reply was in the negative, so I took it for granted that a person who did not tell a lie about (others) the people could never tell a lie about Allah. Then I asked you whether any of his ancestors was a king. Your reply was in the negative, and if it had been in the affirmative, I would have thought that this man wanted to take back his ancestral kingdom. When I asked you whether the rich or the poor people followed him, you replied that it was the poor who followed him. In fact, such are the followers of the apostles. Then I asked you whether his followers were increasing or decreasing. You replied that they were increasing. In fact, this is the result of true faith till it is complete (in all respects). I asked you whether there was anybody who, after embracing his religion, became displeased and discarded his religion; your reply was in the negative. In fact, this is the sign of true faith, for when its cheerfulness enters and mixes in the hearts completely, nobody will be displeased with it. I asked you whether he had ever broken his promise. You replied in the negative. And such are the apostles; they never break their promises. When I asked you whether you fought with him and he fought with you, you replied that he did, and that sometimes he was victorious and sometimes you. Indeed, such are the apostles; they are put to trials and the final victory is always theirs. Then I asked you what he ordered you. You replied that he ordered you to worship Allah alone and not to worship others along with Him, to leave all that your fore-fathers used to worship, to offer prayers, to speak the truth, to be chaste, to keep promises, and to return what is entrusted to you. These are really the qualities of a prophet who, I knew (from the previous Scriptures) would appear, but I did not know that he would be from amongst you. If what you say should be true, he will very soon occupy the earth under my feet, and if I knew that I would reach him definitely, I would go immediately to meet Him; and were I with him, then I would certainly wash his feet.' " Abu Sufyan added, "Caesar then asked for the letter of Allah's Messenger (ﷺ) and it was read. Its contents were: "In the name of Allah, the most Beneficent, the most Merciful (This letter is) from Muhammad, the slave of Allah, and His Apostle, to Heraculius, the Ruler of the Byzantine. Peace be upon the followers of guidance. Now then, I invite you to Islam (i.e. surrender to Allah), embrace Islam and you will be safe; embrace Islam and Allah will bestow on you a double reward. But if you reject this invitation of Islam, you shall be responsible for misguiding the tillers (i.e. your nation). O people of the Scriptures! Come to a word common to you and us and you, that we worship. None but Allah, and that we associate nothing in worship with Him; and that none of us shall take others as Lords besides Allah. Then if they turn away, say: Bear witness that we are (they who have surrendered (unto Him)..(3.64) Abu Sufyan added, "When Heraclius had finished his speech, there was a great hue and cry caused by the Byzantine Royalties surrounding him, and there was so much noise that I did not understand what they said. So, we were turned out of the court. When I went out with my companions and we were alone, I said to them, 'Verily, Ibn Abi Kabsha's (i.e. the Prophet's) affair has gained power. This is the King of Bani Al-Asfar fearing him." Abu Sufyan added, "By Allah, I remained low and was sure that his religion would be victorious till Allah converted me to Islam, though I disliked it."

And Ibn 'Abbas narrated: Abu Sufyan bin Harb told me that Heraclius called for his translator and then asked for the letter of the Prophet (ﷺ), and the former read it (thus):

"In the Name of Allah, the Most Gracious, the Merciful. (This letter is) from Muhammad bin 'Abdullah, to Heraclius. "...O people of the Scripture (Jews and Christians): Come to a word that is just between us and you that we worship none but Allah..." (V.3:64)

Ibn 'Abbas reported that the Messenger of Allah (ﷺ) used to recite in the two (supererogatory) rak'ahs of the dawn prayer:" Say: We believed in Allah and what was revealed to us" and that which is found in Surah Al-i-'lmran:" Come to that word (creed) which is common between you and us" (iii. 64).