Al-Bukhari gave a long narration of the contents of the letter sent by the Prophet to Hercules, king of the Byzantines:
“In the Name of Allah, the Most Beneficent, the Most Merciful. From Muhammad, the slave of Allah and His Messenger to Hercules, king of the Byzantines. Blessed are those who follow true guidance. I invite you to embrace Islam so that you may live in security. If you come within the fold of Islam, Allah will give you double reward, but in case you turn your back upon it, then the burden of the sins of all your people shall fall on your shoulders.
“Say (O Muhammad (PBUH)): ‘O people of the Scripture (Jews and Christians), come to a word that is just between us and you, that we worship none but Allah, and that we associate no partners with Him, and that none of us shall take others as lords besides Allah.’ Then, if they turn away, say: ‘Bear witness that we are Muslims.’ “[The Noble Qur’an 3:64] [Sahih Al-Bukhari 1/4, 5]
Hercules, in turn, asked his translator to communicate his following impression which reveals full conviction in the truthfulness of Muhammad’s Prophethood: ‘I fully realize that Prophets come from noble families; he does not affect any previous example of Prophethood. Since none of his ancestors was a monarch, we cannot then allege that he is a man trying to reclaim his father’s monarchy.
So long as he does not tell lies to people, he is for the more reason, immune to telling lies as regards Allah. Concerning his followers being those deemed weak with numbers ever growing, it is something that goes in agreement with questions of Faith until this latter assumes its full dimensions geographically and demographically. I have understood that no instance of apostasy has as yet appeared among his followers and this points to the bliss of Faith that finds its abode in the human heart. Betrayal, as I see, is alien to him because real Prophets hold betrayal in abhorrence. Bidding worship of Allah with no associates, observance of prayer, honesty and abstinence and prohibition of paganism are traits bound to subject to him all my possessions.
Ihave already known that a Prophet must arise but it has never occurred to me that he will be an Arab from among you. If I was sure I would be faithful to him, I might hope to meet him, and if I were with him, I would wash his feet.’
Hercules then requested that the Prophet’s letter be read. The observations of the emperor and finally the definite and clear-cut exposition of the Islamic message could not but create a tense atmosphere amongst the clergy present at the court. The king did not embrace Islam — for it was differently ordained. However, the Muslim envoy was returned to Madinah with the felicitations of the emperor.