Tafsir Ibn Kathir Surah An Nahl Ayah 104

(Verily, those who do not believe in Allah’s Ayat,) Allah will not guide them, and theirs will be a painful punishment, meaning, the disbelievers and heretics who are known to the people as liars. The Messenger Muhammad , on the other hand, was the most honest and righteous of people, the most perfect in knowledge, deeds, faith and conviction. He was known among his people for his truthfulness and no one among them had any doubts about that – to such an extent that they always addressed him as Al-Amin (the Trustworthy) Muhammad. Thus when Heraclius, the king of the Romans, asked Abu Sufyan about the attributes of the Messenger of Allah , one of the things he said to him was, “Did you ever accuse him of lying before he made his claim” Abu Sufyan said, “No”. Heraclius said, “He would refrain from lying about people and then go and fabricate lies about Allah”