Musnad Ahmad 27:1900

'Abd al-Razzaq narrated to us, Ma'mar informed us, from al-Zuhri, from Salim, from Ibn 'Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) passed by Ibn Sayyad among a group of his companions, among whom was 'Umar ibn al-Khattab, while he was playing with the boys near the fortress of Banu Maghala, and he was a boy. He did not notice until the Messenger of Allah (peace and blessings of Allah be upon him) struck his back with his hand, then said: "Do you bear witness that I am the Messenger of Allah?" Ibn Sayyad looked at him and said: "I bear witness that you are the Messenger of the unlettered." Then Ibn Sayyad said to the Prophet (peace and blessings of Allah be upon him): "Do you bear witness that I am the Messenger of Allah?" The Prophet (peace and blessings of Allah be upon him) said: "I believe in Allah and His messengers." The Prophet (peace and blessings of Allah be upon him) said: "What comes to you?" Ibn Sayyad said: "A truthful one and a liar come to me." The Prophet (peace and blessings of Allah be upon him) said: "The matter has been confused for you." Then the Prophet (peace and blessings of Allah be upon him) said: "I have hidden something for you," and he had hidden for him: {The day the sky will bring a visible smoke} [Ad-Dukhan: 10]. Ibn Sayyad said: "It is Ad-Dukh!" The Prophet (peace and blessings of Allah be upon him) said: "Be off, for you will never exceed your limit." 'Umar said: "O Messenger of Allah, permit me to strike his neck." The Messenger of Allah (peace and blessings of Allah be upon him) said: "If it is he, you will not be given power over him, and if it is not he, there is no good for you in killing him."