Menurut sumber-sumber Islam tradisional, pada tahun 628 Muhammad mengirim surat kepada Heraclius yang mengundangnya masuk Islam.<ref>Siddiqui (2007)</ref> Teks surat kepada Heraclius (Arab: هِرَقْل, diromanisasi: Hiraql), berbunyi sebagai berikut:<ref [12]name="bukhari2">{{cite [13]web|title=Sahih al-Bukhari 2940, 2941 - Fighting for the Cause of Allah (Jihaad) - كتاب الجهاد والسير|url=https://sunnah.com/bukhari:2940|access-date=18 August 2021|website=sunnah.com|publisher=Sunnah.com - Sayings and Teachings of Prophet Muhammad (صلى الله عليه و سلم)}}</ref><ref name="mishkat">{{cite web|title=Mishkat al-Masabih 3926 - Jihad - كتاب الجهاد|url=https://sunnah.com/mishkat:3926|access-date=19 August 2021|website=sunnah.com|publisher=Sunnah.com - Sayings and Teachings of Prophet Muhammad (صلى الله عليه و سلم)}}</ref><ref name="alarabiya2">{{Cite web|date=May [14], 2017|title=In Pictures: Prophet Mohammed's letters that were sent to rulers|url=https://english.alarabiya.net/en/features/2017/05/14/In-Pictures-Prophet-Mohammed-s-letters-to-heads-of-states|website=Al Arabiya English}}</ref>
