[Surah Al-Qalam 68:4]
"Ibn An-Natur was the Governor of llya' (Jerusalem) and Heraclius was the head of the Christians of Sham. Ibn An-Natur narrates that once while Heraclius was visiting ilya' (Jerusalem), he got up in the morning in a bad mood. Some of his priests asked him why he was so upset. Heraclius was a foreteller and an astrologer. He replied, “At night when I looked at the stars, I saw that the leader of those who practice circumcision had appeared (become the conqueror). Who are the ones who practice circumcision?”
The people replied, “Except the Jews, nobody practices circumcision, so you should not be afraid of them (Jews).”
“Just Issue orders to kill every Jew present in the country.”
While they were discussing it, a messenger sent by the king of Ghassan to convey the news of Allah's Messenger (ﷺ) to Heraclius was brought in. Having heard the news, he (Heraclius) ordered the people to go and see whether the messenger of Ghassan was circumcised. The people, after seeing him, told Heraclius that he was circumcised. Heraclius then asked him about the Arabs. The messenger replied, “Arabs also practice circumcision.”
(After hearing that) Heraclius remarked that leader of the 'Arabs had appeared. Heraclius then wrote a letter to his friend in Rome who was as good as Heraclius in knowledge. Heraclius then left for Homs. (a town in Syrian and stayed there till he received the reply of his letter from his friend who agreed with him in his opinion about the emergence of the Prophet (ﷺ) and the fact that he was a Prophet.
After receiving his confirmation, Heraclius invited all the heads of the Byzantines to assemble in his palace at Homs. When they assembled, he ordered that all the doors of his palace be closed. Then he came out and said, “O Byzantines! If success is your desire and if you seek right guidance and want your empire to remain then give a pledge of allegiance to this Prophet (i.e. embrace Islam).”
(On hearing the views of Heraclius) the people ran towards the gates of the palace like onagers but found the doors closed. Heraclius realized their hatred towards Islam and when he lost the hope of their embracing Islam, he ordered that they should be brought back in audience.
(When they returned) he said, “What I previously said was just to test the strength of your conviction and I have seen it.”
The people prostrated before him and became pleased with him, and this was the end of Heraclius's story (in connection with his faith).