Excerpts from "The Sealed Nectar"
Al-Bukhari records a long narration of the contents of the letter sent by the Prophet to Heraclius, emperor of the Byzantines:
"In the name of Allah, the Most Gracious, the Most Merciful.
From Mohammad, the servant of Allah and His messenger, to Heraclius, the king of the Byzantines.
Blessed are those who follow true guidance. I invite you to embrace Islam so that you may live in security. If you come within the fold of Islam, Allah will give you a double reward, but if you turn your back upon it, then the burden of the sins of all your people will fall on your shoulders.
قُلْ يَا أَهْلَ الْكِتَابِ تَعَالَوْا إِلَىٰ كَلِمَةٍ سَوَاءٍ بَيْنَنَا وَبَيْنَكُمْ أَلَّا نَعْبُدَ إِلَّا اللَّهَ وَلَا نُشْرِكَ بِهِ شَيْئًا وَلَا يَتَّخِذَ بَعْضُنَا بَعْضًا أَرْبَابًا مِّن دُونِ اللَّهِ فَإِن تَوَلَّوْا فَقُولُوا اشْهَدُوا بِأَنَّا مُسْلِمُونَ
"Say (O Muhammad): 'O people of Scripture (Jews and Christians), come to a word that is just between us and you, that we worship none but Allah, and that we associate no partners with Him, and that none of us shall take others as lords besides Allah.' Then, if they turned away, say: 'Bear witness that we are Muslims'." [3:64]
Dihyah bin Khalifah Al-Kalbi was ordered to hand the letter to the governor of Busra, who would in turn send it to Caesar.
Incidently Abu Sufyan bin Harb, who at that time had not yet embraced Islam, was summoned to the court and Heraclius asked him many questions about Muhammad and the religion that he preached. The testimony which this open enemy of the Prophet gave regarding the personal excellence of the Prophet's character and the good that Islam was doing for humanity left Heraclius wonder-struck.
Al-Bukhari, on the authority of Ibn 'Abbas, narrated that Heraclius sent for Abu Sufyan and his companions, who happened to be trading in Sham (Syria, Palestine, Lebanon and Jordan) and had come to Iliya' (Baitul-Maqdis). This was during the truce that had been concluded between the polytheists of Quraish and Allah's Messenger Sallallahu Alaihi Wasallam. Heraclius, seated among his chiefs of staff, asked, "Who amongst you is the nearest relative to the man who claims to be a Prophet?". Abu Sufyan relates the story: "I replied, I am the nearest relative to him from amongst the group.' 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) about that man who claims to be a Prophet. If he tells 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."
Abu Sufyan continued: "Muhammad descends from a noble family. No one from his family happened to assume kingship. His followers are those considered weak, with numbers ever-growing. He neither tells lies not betrays others, we fight him and he fights us but with alternate victory. He bids people to worship Allah, alone with no associate, and abandon the beliefs of forefathers. He orders as observed prayer, honesty, abstinence and the maintaining of strong family ties."
Heraclius, on hearing this testimony turned to his translator and ordered him to communicate to us his impression, which revealed full confidence in the truthfulness of Mohammad's prophethood: `I fully realise that Prophets come from noble families; he does not have any previous example of prophethood. Since none of his ancestors was a king, we cannot then claim that he is a man trying to be reclaim his father's kingdom. So long as he does not tell lies regarding people, he is for the more reason, immune to telling lies in regards to Allah. Concerning his followers being those considered weak, with numbers ever-growing, this is the case with faith until it is complete. I have understood that no instance of apostasy has yet appeared among his followers, and this points to the bliss of faith that finds its place in the human heart. Betrayal, as I see, is alien to him because real Prophets hold themselves from betrayal. You said he orders the worship of Allah with no associates, observance of prayer, honesty, abstinence and prohibition of paganism, if this is true, he will soon rule the place beneath my feet. I have already known that a Prophet would arise but it has never occurred to me that he will be an Arab from among you. If I was sure, I would be faithful to him; I might hope to meet him, and if I were with him I would wash his feet.'
Heraclius then requested that the Prophet's letter be read. The observations of the emperor and finally the definite and clear-cut exposition of the Islamic message could only create a tense atmosphere amongst the clergy present at the court. They were ordered to leave."
Abu sufian continued, "While coming out, I said to my companions, "The matter of Ibn Abi Kabshah (i.e., Muhammad) has become so prominent that even the king of Banu Al-Asfar (i.e., the Romans) is afraid of him.' So I continued to believe that Allah's Messenger would be victorious, until Allah made me embrace Islam." The king did not embrace Islam, for it was differently ordained. However the Muslim envoy was returned to Madina with the felicitations of the emperor.
On his way back to Madinah, Dihyah Al-Kalbi was intercepted by people from the tribe of Judham in Hishma, who looted the present sent to the Prophet Sallallahu Alaihi Wasallam. Zaid bin Harithah at the head of 500 men was dispatched to that spot; he inflicted heavy losses on those people and captured 1000 camels, 5000 of their capital and a 100 women and boys. One of the chiefs of Judham who had embraced Islam, filed a complaint with the Prophet Sallallahu Alaihi Wasallam, who gave a positive response to his protest, and ordered that all the spoils and captives be returned.
Most of the authors on the battles of the Prophet state that this event occurred before Al Hudaibiya, however this is an obvious mistake since he Sallallahu Alaihi Wasallam sent the letter to Heraclius after Al-Hudaibiyah. This is why Ibn Al-Qayim said, "It was after Al-Hudaibiyah without a doubt."