Musnad Ahmad 72:1

Hashim ibn al-Qasim narrated to us, Abu Mu'awiyah—meaning Shayban—narrated to us, from Yahya ibn Abi Kathir, from Muhammad ibn Ibrahim, that Ibn 'Abis al-Juhani said: The Messenger of Allah (ﷺ) said: "O Ibn 'Abis, shall I not inform you of the best thing with which those who seek refuge seek refuge?" I said: "Yes, O Messenger of Allah." He said: "Say: 'I seek refuge in the Lord of the daybreak' (Surah Al-Falaq), and say: 'I seek refuge in the Lord of mankind' (Surah An-Nas)."