Mishkat al-Masabih — Hadith #51039

On the authority of Ibn Abbas: The Prophet, may God bless him and grant him peace, wrote to Caesar calling on him to Islam, and he sent his letter to him, Dihya al-Kalbi. He commanded him to give it to the chief of Busra so that he could give it to Caesar, and lo and behold there was in it: “In the name of God, the Most Gracious, the Most Merciful, from Muhammad, the servant of God.” God and His Messenger to Heraclius, the Great of the Romans, peace be upon whoever follows guidance. As for what follows, I invite you as a preacher of Islam. Become a Muslim. Become a Muslim. Become a Muslim. God will give you your reward twice, and if you turn back, then upon you is the sin of the Arisians. (O People of the Book, come to a common word.) It is between us and you that we worship none but God, and do not associate anything with Him, and do not take others as lords besides God. But if they turn away, say: Bear witness that we are Muslims) Agreed upon. And in a narration by Muslim, he said: From Muhammad, the Messenger of God, and he said: “The sin of the Yarisites,” and he said: “With the propaganda of Islam”