What is the authenticity of the story of Amr ibn al-'As's conversion to Islam when he asked the Negus to kill the Messenger of the Messenger of God, whereupon the Negus struck him on the nose saying: "Do you want me to kill the messenger of one upon whom the Great Nāmūs descends?"

The story mentioned in Musnad Imam Ahmad and other collections, with a good chain of narration, is narrated by Amr ibn al-Aas. He recounts that after the Battle of the Trench, he considered joining the Negus with a group of Quraysh, fearing the ascendancy of Muhammad (peace be upon him), so they could be safe with him. When they arrived at the Negus's court, Amr ibn Umayyah al-Damari came to him as a messenger from the Prophet (peace be upon him). Amr ibn al-Aas then asked the Negus to hand him over so he could kill him. The Negus became angry and refused, explaining to Amr ibn al-Aas that Muhammad was a true messenger, and that what came to him was the great Nāmūs (Divine Law/Angel Gabriel) that had come to Moses. At that point, Amr ibn al-Aas asked the Negus to pledge allegiance to him (the Prophet) in Islam, which the Negus did. Then Amr ibn al-Aas set off towards the Prophet (peace be upon him) to declare his Islam. He met Khalid ibn al-Walid and Uthman ibn Talhah just before the Conquest, and they too were going to embrace Islam, so they all became Muslim. Amr ibn al-Aas pledged allegiance to the Prophet (peace be upon him) on the condition that his past sins would be forgiven. The Prophet (peace be upon him) then informed him that Islam and Hijrah (emigration) erase previous sins.