Musnad Ahmad 482:6

Al-Walid ibn Muslim narrated to us, he said: Ibn Jabir narrated to us, from al-Qasim Abu Abd al-Rahman, from Uqbah ibn Amir, who said: While I was leading the Messenger of Allah (peace and blessings of Allah be upon him) by the reins in one of those mountain passes, he said to me: "O Uqbah, will you not ride?" He said: I held the Messenger of Allah (peace and blessings of Allah be upon him) in too high esteem to ride his mount. Then he said: "O Uqbah, will you not ride?" He said: I feared that it might be an act of disobedience. He said: So the Messenger of Allah (peace and blessings of Allah be upon him) dismounted, and I rode for a little while, then he mounted. Then he said: "O Uqbah, shall I not teach you two surahs that are among the best two surahs that people recite?" He said: I said: Yes, O Messenger of Allah. He said: So he taught me: "Say, I seek refuge in the Lord of the daybreak" (Al-Falaq) and "Say, I seek refuge in the Lord of mankind" (An-Nas). Then the prayer was called, and the Messenger of Allah (peace and blessings of Allah be upon him) went forward and recited them. Then he passed by me and said: "How did you see them, O Uqbah? Recite them whenever you go to sleep and whenever you wake up." Abu Abd al-Rahman said: "He is Uqbah ibn Amir ibn Abis, and it is said ibn Abs al-Juhani."