The letter of the Prophet ﷺ to Heraclius read, "In the name of Allah, the Most Gracious, the Most Merciful. From Muhammad, the Messenger of Allah, to Heraclius, the great ruler of the Romans. Peace be upon whoever follows the guidance. I invite you with the call of Islam. Accept Islam and you will be safe, and Allah will grant you your reward twice over. But if you turn away, then upon you is the sin of your subjects. 'Say, People of the Book, come to a word common between us and you, that we worship none but Allah, associate nothing with Him, and take not one another as lords besides Allah. But if they turn away, then say, Bear witness that we are Muslims.' [Aal Imran 3:64]"
كان في رسالة النبي ﷺ إلى هرقل: بسم الله الرحمن الرحيم، من محمد رسول الله إلى هرقل عظيم الروم. سلام على من اتبع الهدى أما بعد: فإني أدعوك بدعاية الإسلام، أسلم تسلم، وأسلم يؤتك الله أجرك مرتين، وإن توليت فإن عليك إثم الأريسيين. {قل يا أهل الكتاب تعالوا إلى كلمة سواء بيننا وبينكم ألا نعبد إلا الله ولا نشرك به شيئا ولا يتخذ بعضنا بعضا أربابا من دون الله فإن تولوا فقولوا اشهدوا بأنا مسلمون} [سورة آل عمران: ٦٤].
Bukhari related it in the Tafsir (4553), and Muslim in the Jihad (1773), both from the hadith of Abdul-Razzaq, who said, Mamar informed us, from Zuhri, from Abdullah bin Abdullah bin Utbah, from Ibn Abbas, that Abu Sufyan informed him directly from his own mouth, saying (then he mentioned the hadith).His saying, "the Arisiyyin," is the plural of Arisi, which is derived from Aris, on the pattern of faeel. Ibn Sidah said, Aris means the cultivator, that is, the farmer, according to Thalab, while according to Kuraa, Aris means the ruler. Other interpretations of it have also been given, and it is a Levantine expression.See Fath al-Bari (1/39).