Musannaf Ibn Abi Shayba 21:154

Ghundar narrated to us, from Shu'bah, from Ya'la ibn 'Ata, who said: I heard 'Amr ibn 'Asim narrating that he heard Abu Hurayrah saying: Abu Bakr said to the Prophet, may Allah bless him and grant him peace: "Inform me of something I should say when I reach the morning and when I reach the evening." He said: "Say: 'O Allah, Knower of the unseen and the witnessed, Creator of the heavens and the earth, Lord of everything and its Sovereign, I bear witness that there is no god but You. I seek refuge in You from the evil of my soul, and from the devil and his shirk (polytheism/associating partners with Allah).' Say it when you reach the evening, when you reach the morning, and when you take to your bed."