Narrated Abdullah ibn Abbas: The Prophet (ﷺ) wrote a letter to Heraclius: "From Muhammad, the Messenger of Allah, to Hiraql (Heraclius), Chief of the Byzantines. Peace be to those who follow the guidance." Ibn Yahya reported on the authority of Ibn Abbas that AbuSufyan said to him: We then came to see Hiraql (Heraclius) who seated us before him. He then called for the letter from the Messenger of Allah (ﷺ). Its contents were: "In the name of Allah, the Compassionate, the Merciful, from Muhammad the Messenger of Allah, to Hiraql, chief of Byzantines. Peace be to those who follow the guidance. To proceed

English translation · Sunan Abu Dawud