Abu Dawud Book 2, Hadith Number 1457.
Chapter : O surah alfatihah and surah annas.
Narated By Uqbah ibn Amir : I was driving the she-camel of the Apostle of Allah (PBUH) during a journey. He said to me: Uqbah, should I not teach you two best surahs ever recited? He then taught me: “Say, I seek refuge in the Lord of the dawn,” and “Say, I seek refuge in the Lord of men.” He did not see me much pleased (by these two surahs).
When he alighted for prayer, he led the people in the morning prayer and recited them in prayer. When the Apostle of Allah (PBUH) finished his prayer, he turned to me and said: O Uqbah, how did you see.