Musnad Ahmad 482:13

Yahya ibn Sa'id narrated to us, from Isma'il, who said: Qays narrated to me, from 'Uqbah ibn 'Amir, from the Prophet, may Allah bless him and grant him peace, who said: "Verses have been revealed to me, the likes of which have not been seen: 'Say, I seek refuge in the Lord of mankind' to the end of the surah, and 'Say, I seek refuge in the Lord of the daybreak' to the end of the surah."