Musnad Ahmad 32:776

Hajjaj narrated to us, Laith narrated to us, Sa'id ibn Abi Sa'id narrated to me, from Sharik ibn Abdullah ibn Abi Namir, that he heard Anas ibn Malik saying: While we were sitting with the Messenger of Allah (peace and blessings of Allah be upon him) in the mosque, a man entered on a camel, made it kneel in the mosque, and tied its leg. Then he said: "Which of you is Muhammad, the Messenger of Allah?" The Messenger of Allah (peace and blessings of Allah be upon him) was reclining among them. We said: "This white man who is reclining." The man said: "O son of Abdul-Muttalib." The Messenger of Allah (peace and blessings of Allah be upon him) said to him: "I have answered you." The man said: "O Muhammad, I am going to ask you and be stern in my questioning, so do not find fault with me in yourself." He said: "Ask whatever seems good to you." The man said: "I adjure you by your Lord, and the Lord of those who were before you, has Allah sent you to all of mankind?" The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Allah, yes." He said: "I adjure you by Allah, has Allah commanded you that we pray the five prayers during the day and the night?" He said: "O Allah, yes." He said: "I adjure you by Allah, has Allah commanded you that we fast this month of the year?" The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Allah, yes." He said: "I adjure you by Allah, has Allah commanded you to take this charity from our wealthy ones and distribute it among our poor ones?" The Messenger of Allah (peace and blessings of Allah be upon him) said: "O Allah, yes." The man said: "I have believed in what you have brought, and I am a messenger from those behind me of my people. I am Dammam ibn Tha'labah, the brother of Banu Sa'd ibn Bakr."