A man heard another man reciting "Say, He is Allah, One" He was repeating it. When the next morning came, he went to the Messenger of Allah (ﷺ) and mentioned to him. The man tool it (this surah) as a small one. The Prophet (ﷺ) said: By Him in Whose Hand is my life, it is equivalent to a third of the Qur'an.
Sunan Abi Dawud Book 8, Hadith 46
← Previous Hadith The Messenger of Allah (ﷺ) said: Abu al-Mundhir, which verse of Allah's Book that you have is creates ? I replied: Allah and His Apostle know best. He said: Abu al-Mundhir, which verse of Allah's that you have is greatest ? I said: Allah, there is no god but He, the Living, the Eternal. Thereupon he struck me on the beast and said: May knowledge be pleasant for you, Abu al-Mundhir.

Sunan Abi Dawud Book 8, Hadith 45 Next Hadith → I was driving the she-camel of the Messenger of Allah (ﷺ) 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 Messenger of Allah (ﷺ) finished his prayer, he turned to me and said: O Uqbah, how did you see.

Sunan Abi Dawud Book 8, Hadith 47