Musannaf Ibn Abi Shaybah

Hazrat Amr bin Abasah narrates that when a person, having performed ablution, lies down on his bed and continues to remember Allah until he falls asleep, and upon waking up, the first thing he says is, "O Allah! You are pure, there is no deity except You, forgive me," then he emerges from his sins just as a snake sheds its skin.