Sayyiduna Uqbah bin Amir al-Juhani (may Allah be pleased with him) said: I was leading the she-camel of the Messenger of Allah (peace and blessings be upon him) on a journey when he (peace and blessings be upon him) said: "O Uqbah! Shall I not teach you two surahs that are the best surahs ever recited?" I said: Certainly, O Messenger of Allah! Teach me. So he (peace and blessings be upon him) taught me Surah al-Nas and Surah al-Falaq, but he did not see me impressed by them. Then when he (peace and blessings be upon him) dismounted, he led the people in the morning prayer with these two surahs, and when he finished the prayer he turned to me and said: "O Uqbah! How did you find them?"
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 14997