Sahih Bukhari narrates:

The Prophet ﷺ sent letters of invitation to Islam to the rulers of other countries along with Dihya bin Khalifah al-Kalbi . The Companion went to the Roman empire, too. The ruler read the letter and called upon the people of Quraish who were there in his country for business. He said, “A day will come when the followers of this Prophet will capture Rome and will rule over it,” He continued, “After knowing about this Prophet, I have only one desire; to go to Madinah and pour water when he performs wudhu and lift his shoes when he walks out.”

The Prophecy of the advent of the Prophet ﷺ was not a secret. Imam Muhammed Ibn Ishaq author of Sahibul Magazi narrates:

Dihya bin Khalifah al-Kalbi was a companion who was sent to Heraclius with the letter of the Prophet ﷺ . After seeing the letter Heraclius said, “Why have you come to show me this letter? By Allah! I know very well that your companion whose letter you are carrying, is a Messenger sent by Allah. He is the same Prophet who we were waiting for. We have found him mentioned in our Books.”

He then continued, “If I did not fear my people (killing me), I would have gone to Madinah and accepted his Prophethood. Go to Magatir and meet my senior-most religious scholar. If he accepts Islam, the entire Roman civilization will accept Islam.”

Dihya bin Khalifah al-Kalbi (May Allah be pleased with him) met the senior-most priest and he responded, “The man who has sent you is a real Prophet and I have read all the signs of his prophethood in our Books. Our Book has even mentioned his name.”

Religious Leader Lynched by Mob for becoming Muslim

Saying this, the priest removed his black robe and wore a white one. He then left his court and went to the largest church. A large gathering was present. He went towards them and announced, “O people of Rome! I have received a letter from Ahmed and he has invited us to Islamic monotheism. He is the same Ahmed whose advent was foretold by Jesus and we were instructed to believe in him and obey him. I believe that there is no deity except Allah and Mohammed is His Messenger.”

The moment the people heard it, they rushed to their head priest and killed him. Dihya bin Khalifah al-Kalbi (May Allah be pleased with him) then returned to Heraclius and reported the incident. He said, “I had already told you. I, too, fear the same end if I declare my faith. People respected the chief priest more than me, yet they killed him. Had the people of Rome accepted the faith. I would have accepted, too.”

This is what the Qur’an mentions in Surah al Araf:

 Those who follow the Messenger, the unlettered prophet, whom they find written in what they have of the Torah and the Gospel, who enjoins upon them what is right and forbids them what is wrong and makes lawful for them the good things and prohibits for them the evil and relieves them of their burden and the shackles which were upon them. So they who have believed in him honored him, supported him and followed the light which was sent down with him - it is those who will be the successful.

Surah al Araf, verse 157

Despite the fact that the Roman Emperor, the Chief Priest of the Empire and governors were desperately waiting for the Prophet mentioned in their Books, they could not accept the faith due to their fear.

They claimed, “We are waiting for the prophet about whom we read in our religious books,” but failed to accept Islam.