Musnad Abu Ya'la al-Mawsili 244:18

Wahb ibn Baqiyyah narrated to us, Khalid informed us, from Muhammad ibn ‘Amr, from his father, from his grandfather, who said: ‘Amr ibn al-‘As said: An army of the Muslims went out, and I was their commander, until we descended upon Alexandria. One of their great men said to me: "Send out a man to me so that I may speak to him and he may speak to me." I said: "No one shall go out to him except me." So I went out with his translator until two pulpits were placed for us. He said: "Who are you?" We said: "We are the Arabs. We are the people of the thorns and the acacia. We are the people of the House of God. We were the people with the narrowest land and the harshest life. We used to eat carrion and blood, and some of us would raid others—the worst life that people ever lived. Then a man emerged among us who was not, on that day, the most noble of us in status, nor the wealthiest of us. He said: 'I am the Messenger of God to you.' He commanded us with things we did not know and forbade us from what we and our fathers were upon. We despised him, denied him, and rejected his speech, until a people from other than us went out to him and said: 'We believe you, we have faith in you, we follow you, and we will fight whoever fights you.' So he went out to them, and we went out to him, and we fought him. He killed us, prevailed over us, and defeated us. Then he turned to those of the Arabs who were near him and fought them until he prevailed over them. If those of the Arabs who are behind me knew of the life you are in, not one would remain except that he would come to you to share with you in the life you are in." He laughed, then said: "Indeed, the Messenger of God, may God bless him and grant him peace, spoke the truth. Our messengers came to us with the like of what your Messenger came with, and we were upon it until kings appeared among us. They began to act according to their own desires and abandoned the command of the prophets. If you hold fast to the command of your Prophet, no one will fight you except that you will defeat them, and no one will contend with you except that you will prevail over them. But if you do as we did—abandoning the command of your Prophet and acting as they acted according to their own desires—then we will be left between you and ourselves, and you will not be greater in number than us, nor stronger in power than us." ‘Amr ibn al-‘As said: I have never spoken to a man more mindful than him.