The tides of events, sometimes, foretell about the future developments in history. These prophecies get special importance if they are from the source of revelation. In such cases, we ought to receive such implications, and after pondering over them, we have to acknowledge them, and prepare for their occurrence. The appointment (al-Mab'ath) of Prophet Mohammad (saw) to prophetic mission was among the subjects which were foretold from long before.
Noble Qur'an explicitly states that 'the People of the Book read about him and his traits, and they are aware that their prophets have elucidated the appearance of such leader.'
"Those who follow the Apostle-Prophet, the Ummi, whom they find written down with them in the Tawrat and the Injeel, (who) enjoins them good and forbids them evil, and makes lawful to them the good things and makes unlawful to them impure things, and removes from them their burden and the shackles which were upon them..." ( Noble Qur'an, 7:157)
"And when there came to them a Book from Allah verifying that which they have, and aforetime they used to pray for victory against those who disbelieve, but when there came to them (Prophet) that which they did not recognize, they disbelieved in him..." ( Noble Qur'an, 2:89)
Therefore, the Jewish scholars, the Christian priests, and Arab geomancers knew about the emergence of Prophet Mohammad (saw) from the clues in the Testaments.
Based on these prophecies, when Prophet Mohammad (saw), in the 7th AH, wrote invitation letters to the powerful governors of the world and among them is Heraclius, the emperor of Byzantine of Eastern Roman Empire.
The Byzantine Empire is also known as the Eastern Roman Empire, for it was in fact a continuation of the Roman Empire into its eastern part. Heraclius was the ruler between 610 - 641CE.
Abu Sufyan ibn Harb a leader of the tribe of Quraish and the arch enemy of Prophet Mohammad (saw), by coincidence, he is in Syria (Shaam) on a business trip, when the Prophet Mohammad's (saw) letter of invitation reached Heraclius, the emperor of Byzantine of Eastern Roman Empire. Heraclius, at the time was in his court at Constantinople - modern day Istanbul or Jerusalem celebrating his victory over the Persians.
Note: Abu Sufyan ibn Harb become so called Muslim only after the conquest of Makkah in 630 CE (8 AH) and this incident is from around 628CE.
Heraclius read the letter through an interpreter and then asked the people in his court, to find out if there was someone in the city, who knew Prophet Mohammad (saw). Heraclius agent reached Abu Sufyan ibn Harb with his companions was brought into the court.
Heraclius: "What kind of family does Muhammad belongs to?" asked
Abu Sufyan ibn Harb: "Noble family", replied
Heraclius: "Has there been a king in his family?" asked
Abu Sufyan ibn Harb: "No," replied
Heraclius: "Are the people who have accepted his religion poor or rich?" questioned again
Abu Sufyan ibn Harb: "The people of higher class are against him, and people of middle class and lower class support him and accept his religion", replied
Heraclius was now becoming more and more interested and he went on asking questions.
Heraclius: "Are his followers on the increase or decrease?"
Abu Sufyan ibn Harb: "Increasing", replied shortly
Heraclius: "Have you known him to tell lies"? asked
Abu Sufyan ibn Harb: "No, he is an honest person", admitted
Heraclius: "Does he ever go against his convents?" once again asked
Abu Sufyan ibn Harb: "Not so far. But we have to see whether he carries out the new agreement made between us and him", answered lengthily for a change
Heraclius: "Have you ever fought him in wars?" questioned
Abu Sufyan ibn Harb: "Yes", answered
Heraclius: "What has been the result?" asked, getting more and more interested
Abu Sufyan ibn Harb: "Sometimes we have won, sometimes he", replied
Heraclius: "What does he teach?" asked
Abu Sufyan ibn Harb: "Worship One God, join no partners with Him, carry out your prayers, be chaste, speak the truth and keep union with your relatives", answered
Even surprised at his own answer as it sounded like he was preaching Islam, Heraclius stood up and said, "If all you said is true, then I am sure that this Prophet's Kingdom will reach here where I am standing. I was certain that a Prophet was coming, but I didn't know that he would be born in Arabia. If I were to go there, I would embrace Islam and wash the Prophet's feet with my own hands."
This was the way in which Prophet Mohammad (saw) spread Islam. Prophet Mohammad (saw) impressed them by his truthfulness, honesty, noble character and dedication in the service of Allah (SWT). Prophet Mohammad (saw) did not compel people to accept Islam under threat of waging wars, nor did he compel people to accept Islam by the force of the sword. Prophet Mohammad (saw) fought only in defense, and only when the enemies waged war on him.