Musannaf Ibn Abi Shayba 1:1267

Yazid ibn Harun narrated to us, he said: Al-Awwam informed us, from Shahr ibn Hawshab, from Amr ibn Abasah, who said: When a man goes to his bed in a state of purity and remembers Allah until his eyes overcome him, and the first thing he says when he wakes up is, "Glory be to You, there is no god but You, forgive me," he sheds his sins just as a snake sheds its skin.