Abu Sufyan Sakhr bin Harb (May Allah be pleased with him) mentioned Heraclius in a long Hadith and said:
Heraclius asked me, "What does this Prophet (ﷺ) teach you?" I said, "He orders us to worship Allah Alone and not to associate a thing with Him in worship, to discard what our ancestors said, to perform the Salat (prayer), speak the truth, and maintain the ties of kinship".[Al-Bukhari and Muslim].