Following the Treaty of Hudaybiyyah, the Prophet Muhammad (PBUH) saw an opportunity to extend the message of Islam beyond the Arabian Peninsula. In this period, he is reported to have sent letters to various rulers, inviting them to embrace Islam. The most well-documented of these is the letter sent to Heraclius, the Byzantine Emperor, which is preserved in a sahih narration. This letter was delivered by Dihyah al-Kalbi, and it prompted Heraclius to question Abu Sufyan, who was then in the Byzantine-controlled territory for trade, about the Prophet and his message.
Heraclius's inquiry into the character and claims of the Prophet, as recounted in Sahih al-Bukhari, reveals a moment of curiosity and contemplation. Heraclius asked Abu Sufyan about the lineage, honesty, and following of Muhammad, seeking to understand the new religious movement. Despite Abu Sufyan's enmity towards the Prophet at the time, he could not deny Muhammad's noble qualities and growing influence. Heraclius's reaction to the letter, as recorded, was one of cautious interest, though he ultimately did not accept Islam.
While the letter to Heraclius is well-attested, the reports of letters to other rulers, such as Chosroes of Persia, the Negus of Abyssinia, and the ruler of Egypt, rest on Seerah accounts without chains of narration. These accounts suggest a broader diplomatic effort, but their details and authenticity are less certain. The Prophet's initiative in reaching out to these rulers signifies a strategic expansion of Islam's reach and a recognition of the interconnectedness of the region's political landscape.