He then called for the letter of the Messenger of Allah ﷺ which he had sent with Dihya to the ruler of Bostra, and handed it to Heraclius, who read it. It contained the following:In the name of Allah, the Most Merciful, the Bestower of Mercy. From Muhammad, the servant of Allah and His Messenger, to Heraclius, ruler of the Romans. Peace be upon whoever follows the guidance. To proceed, I call you with the call of Islam. Accept Islam and you will be safe, and Allah will grant you your reward twice over… the hadith continues.
في حديث طويل في قصة هرقل:
ثم دعا بكتاب رسول الله ﷺ الذي بعث به دحية إلى عظيم بصرى، فدفعه إلى هرقل، فقرأه، فإذا فيه: بسم الله الرحمن الرحيم. من محمد عبد الله ورسوله إلى هرقل عظيم الروم، سلام على من اتبع الهدى، أما بعد؛ فإني أدعوك بدعاية الإسلام، أسلم تسلم، يؤتك الله أجرك مرتين… الحديث.
Bukhari narrated it in the Beginning of Revelation (7), and Muslim in Jihad (1773:74), both through Zuhri, who said, Ubaydullah bin Abdullah bin Utba bin Masud told me that Abdullah bin Abbas told him that Abu Sufyan bin Harb told him, and he related it.