Peaceful conditions followed the treaty of Huday- biyyah and the Messenger of Allah wrote letters to foreign sovereigns and to Arab chieftains, inviting them to accept Islam. He took great care to select a suitable messenger for each king and the letters were painstakingly prepared. He was told that foreign kings would not accept any letter without a seal so he had a silver signet ring made on which was inscribed, 'Muhammad, Messenger of Allah.'

Among the kings he contacted were the Byzantine emperor, Heraclius, the Persian emperor, Chosroes Parvez, the Negus, King of Abyssinia, and Muqawqis, King of Egypt.

Heraclius, the Negus and Muqawqis received their letters with respect and gave courteous replies. Heraclius wanted to know more about the Prophet and dispatched men to find out all they could. Abu Sufyan happened to be in Ghazzah on a business trip and he was presented to the king. Heraclius proved to be an intelligent examiner who knew the history of religion and the qualities and behaviour of the Prophets. He had studied how nations reacted to them and how and when Allah would send them. Abu Sufyan was truthful in his answers in the tradition of the early Arabs who considered it beneath their dignity to tell a lie.

When Heraclius heard Abu Sufyan's answers, he was certain that Muhammad was the Prophet of Allah. He said, 'If what you say is true, he will come to possess the place on which my two feet are standing. I knew that one was due to come forth but I did not think that he would come from you. If I knew that I could reach him, I would set out to meet him. If I was with him, I would wash his feet.' 

He summoned the Roman generals to the castle and commanded that the doors be shut. Then he went to them, declaring, 'O Romans! If you want success and right guidance and to establish and strengthen your kingdom, give homage to this Prophet.'

They disliked what he was saying and tried to leave but they found that the doors were locked. When Heraclius saw their reaction, he despaired of their faith. He said, 'Return those people to me,' and to them he repeated, 'What I said before was to test your faith. Now I have seen it.' 

They prostrated before him and were pleased with what he had said.

Heraclius had preferred his kingdom to Islam. Wars and battles continued between him and the Muslims during the caliphate of Abu Bakr and 'Umar when he lost both his kingdom and his power.

The Negus and the Muqawqis were most courteous to the envoys sent by the Messenger of Allah. The Muqawqis sent him gifts, including two slavegirls. One of them was Mariah, the mother of Ibrahim, the son of the Messenger of Allah.

When Chosroes, the emperor of Persia, read the letter, he tore it up indignantly, 'How dare this person who is my slave write to me like this!' he demanded.

When the Messenger of Allah heard about Chosroes' reaction, he replied, 'Allah will shatter his kingdom.'

Chosroes commanded Badhan, his governor in Yemen, to bring the Messenger of Allah to him. Badhan delegated the task to Babawayh. When Babawayh came to the Messenger of Allah in Madinah, he said, 'The King of Kings, Chosroes, wrote to King Badhan commanding him to send out men to bring you to him. He has sent me to fetch you.'

However, the Messenger of Allah told him that Allah had given Shirawayh power and he would kill his father Chosroes. And indeed that was the truth. Allah shattered the Sassanid kingdom which had existed for four hundred years, and gave the Muslims power over it. He guided the Persian people to Islam.