Editorial note: Authenticated hadith preserve the letter to Heraclius and the report of the letter sent to Khosrau. Lists of additional rulers, messengers and responses vary in later historical works, so this article gives priority to the best-attested reports.
A message beyond Arabia
After the Treaty of Hudaybiyyah created a period of reduced conflict with Mecca, the Prophet Muhammad sent messengers carrying invitations to rulers beyond the immediate Muslim community. These letters belong to a new stage in the prophetic mission. The invitations now reached beyond families, tribes and neighboring settlements. They addressed political leaders connected with the great powers surrounding Arabia.
The best-documented example is the letter to Heraclius, the Byzantine emperor. Sahih al-Bukhari preserves the account within a longer report from Abu Sufyan, who was not yet Muslim when Heraclius questioned him about Muhammad’s character and followers. The letter identifies its sender as Muhammad, servant and messenger of God, offers peace to the one who follows guidance and invites Heraclius to Islam.
A shared scriptural appeal
The letter to Heraclius cites Quran 3:64, calling the People of the Book to a common word: worship of God alone without partners and refusal to treat human beings as lords beside God. This quotation matters because it shows the invitation’s theological center. The message was not merely a request for political recognition. It was a call to monotheism framed in language addressed directly to Jewish and Christian audiences.
The report also shows a formal diplomatic process. A messenger carried the letter through official channels before it reached the emperor. Heraclius then questioned Abu Sufyan about Muhammad’s lineage, truthfulness, followers and conduct. Whatever conclusion readers draw about Heraclius’s personal response, the narration shows people outside Arabia examining the claim of prophethood.
The letter to Khosrau
Another authenticated report concerns Khosrau, ruler of the Sasanian Empire. Abdullah ibn Hudhafa carried the letter and delivered it through the ruler of Bahrain. The narration says that Khosrau tore it apart after reading it. This reaction stands in contrast to the extended inquiry attributed to Heraclius.
However, the two accounts do not support a simple contrast between one ruler accepting the message and another rejecting it. The surviving hadith describes reactions, questions and the transmission of letters; it does not justify inventing private beliefs that the sources do not establish. Responsible history keeps the documented core clear while acknowledging where later narratives supply additional detail.
Why the letters mattered
- Universal scope: the invitations expressed that the message was not limited to one tribe or language.
- Peaceful communication: messengers and written arguments carried the invitation across political borders.
- Clear theology: the letter to Heraclius centered worship of God alone and cited a Quranic appeal to the People of the Book.
- Personal accountability: the letters addressed rulers as decision-makers whose influence affected others.
- Historical transition: the correspondence shows the Medinan community acting with growing diplomatic confidence.
Reading the reports carefully
Popular retellings sometimes present a long, fixed list of letters with exact wording and dramatic reactions for every recipient. The evidence is not equally strong for every item. The letter to Heraclius has unusually detailed support in Sahih al-Bukhari and Sahih Muslim, while Sahih al-Bukhari also preserves the report about Khosrau. Claims beyond those reports should identify their historical source and avoid presenting later reconstruction as certain.
With that distinction in place, readers can examine the letters as both religious invitations and historical acts of communication. They carried a concise statement of faith, used recognized diplomatic channels and announced that the Muslim community understood its responsibility in international terms.
