Abu Dawud Book 2, Hadith Number 1458.
Chapter : O surah alfatihah and surah annas.
Narated By Uqbah ibn Amir : White I was travelling with the Apostle of Allah (PBUH) between al-Juhfah and al-Abwa’, a wind and intense darkness enveloped us, whereupon the Apostle of Allah (PBUH) began to seek refuge in Allah, reciting: “I seek refuge in the Lord of the dawn,” and “I seek refuge in the Lord of men.”
He then said: Uqbah, use them when seeking refuge in Allah, for no one can use anything to compare with them for the purpose.
Uqbah added: I heard him reciting them when he led the people in prayer.