The text of the letter to Heraclius, as transmitted by Muslim historians, reads as follows:

من محمد بن عبد الله إلى هرقل عظيم الروم: سلام على من اتبع الهدى، أما بعد فإنى أدعوك بدعوة الإسلام . أسلم تسلم ويؤتك الله أجرك مرتين ، فإن توليت فإن عليك إثم الأريسيِّين.

{قُلْ يَا أَهْلَ الْكِتَابِ تَعَالَوْا إِلَىٰ كَلِمَةٍ سَوَاءٍ بَيْنَنَا وَبَيْنَكُمْ أَلَّا نَعْبُدَ إِلَّا اللَّهَ وَلَا نُشْرِكَ بِهِ شَيْئًا وَلَا يَتَّخِذَ بَعْضُنَا بَعْضًا أَرْبَابًا مِّن دُونِ اللَّهِ ۚ فَإِن تَوَلَّوْا فَقُولُوا اشْهَدُوا بِأَنَّا مُسْلِمُونَ} [سورة آل عمران : 64].

In the name of God, the Most Merciful, the Bestower of all Mercy

From Muhammad, son of Abdullah to Heraclius the Leader of the Romans:

Peace be upon he who follows the guidance.

Furthermore, I invite you with the invitation of peace. If you submit then you will find safety and God will double your reward. If you turn away, you will bear the Arians’ sins.

“O People of the Scripture! Come to a common word between us and you: that we shall worship none but God, and that we shall ascribe no partner unto Him, and that none of us shall take others for lords beside God. And if they turn away, then say: Bear witness that we are they who have surrendered (unto Him).

— Quran, Chapter: Aal Imran “The House of Joachim” 3:64