"In the Name of Allâh, the Most Beneficent, the Most Merciful.
From Muhammad, the slave of Allâh 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, Allâh 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 Allâh, and that we associate no partners with Him, and that none of us shall take others as lords besides Allâh.’ Then, if they turn away, say: ‘Bear witness that we are Muslims.’ " [Al-Qur'an 3:64][Sahih Al-Bukhari 1/4,5]