Daghater, the archbishop, lived In the period of Heracles. The reason behind his acceptance of Islam are the same that cause Abdullah Bin Salam, the rabbi of the Jews and their master, to accept Islam. This is what He found from the conformance between the glad tidings in the Bible and the characteristics of the prophet Mohammad PBUH, his location, and his time.
The prophet Mohammad PBUH sent Duhiah Al-Kalbi with a message to invite Heracles, the greatest of the Romans to accept Islam, Heracles read that message which included,
"In the name of Allah,
From Mohammad, the messenger of Allah, to Heracles, the greatest of the Romans, peace be upon those who follow the guidance.
I invite you to accept Islam, if you adopt Islam, you will guarantee the peace. Also, You will have double reward from Allah if you embrace Islam. But if you refuse you will carry your sins and the Arian's sin . Then, he recited, (O Mohammad ): " O people of the Scripture ( Jews and Christians): come to a word that is just between us and you, that we worship none but Allah(Alone), and that we associate no partner with Him, and that none of us shall take others as lords besides Allah. Then, if they turn away, say: '' Bear witness that we are Muslims."
When Heracles finished reading the message, the noise and the argument sharply raised {narrated by Al-Bukary, Hadeeth 4278}
Then, Heracles sent this message to the archbishop in his kingdom to counsel him about it. The archbishop replayed, "this is what we have waited and what Jesus has told us in the good tidings". He added, "I believed and I will follow him". The Kaisar said, if I do that, it means my property will be gone.
After that, the archbishop said to the messenger of the prophet Mohammad PBUH " take this message to the Prophet, deliver my greeting to him and tell him that I, the archbishop, bear witness that there is no Gog but Allah and Mohammad is the messenger of Allah. I have believed in him and accepted Islam but my people have denied what I have done. Then, the archbishop went out to them and they killed him.
Then, Duhiah returnd to Heracles and said, "I told you we fear from them and in their view Daghater is more important then me.{ Al-Imam Bin Hajer in Fath Al-Bari Sahih Al-Bukary explaination}.
Arians are the people of Jesus's true message and waiting for the prophet Mohammad PBUH.
