Musnad Ahmad 658:179

Waki’ narrated to us, from Sufyan, from Abu Ishaq, from al-Bara’, that the Prophet, peace and blessings of Allah be upon him, said to a man: "When you go to your bed, say: O Allah, I have submitted my face to You, and I have entrusted my back to You, and I have committed my affair to You, out of desire and fear of You. There is no refuge and no escape from You except to You. I have believed in Your Book which You revealed, and in Your Prophet whom You sent. For if you die, you will die upon the natural disposition (fitrah), and if you wake up, you will wake up having attained good."