Musannaf Ibn Abi Shayba 21:185

Ja'far ibn 'Awn narrated to us, from al-Afriqi, from 'Abdullah ibn Yazid, from 'Abdullah ibn 'Amr, that the Prophet (may Allah bless him and grant him peace) said to a man from the Ansar: "How do you say when you want to sleep?" He said: "I say: 'In Your name, my Lord, I have laid down my side, so forgive me.'" He said: "You have been forgiven."