Heraclius sent for him along with a group from Quraysh who were trading in Syria. They came to him, and he mentioned the hadith. He said, "Then he called for the letter of the Messenger of Allah ﷺ, and it was read aloud. It contained the following, 'In the name of Allah, the Most Merciful, the Most Compassionate. From Muhammad, the servant of Allah and His Messenger, to Heraclius, the leader of the Romans. Peace be upon whoever follows the guidance. To proceed.'"
حدثنا سويد أنبأنا عبد الله أنبأنا يونس عن الزهري أخبرني عبيد الله بن عبد الله عن ابن عباس أنه أخبره أن
أن هرقل أرسل إليه في نفر من قريش وكانوا تجارا بالشام فأتوه فذكر الحديث قال ثم دعا بكتاب رسول الله ﷺ فقرئ فإذا فيه بسم الله الرحمن الرحيم من محمد عبد الله ورسوله إلى هرقل عظيم الروم السلام على من اتبع الهدى أما بعد
Agreed upon [by Bukhari and Muslim]. Bukhari narrated it in the Book of Seeking Permission, Chapter on How to Write a Letter to the People of the Book, hadith no. 6260, from the hadith of Ibn Mubarak, and Muslim narrated it, hadith no. 1773, from the hadith of Zuhri, with the same wording.