Musnad Ahmad 658:182

'Abd al-Rahman and Ibn Ja'far narrated to us, they said: Shu'bah narrated to us, from Abu Ishaq, he said: I heard al-Bara' ibn 'Azib saying: The Prophet, peace and blessings of Allah be upon him, advised a man that when he takes to his bed, he should say: "O Allah, I have submitted my soul to You, and I have turned my face toward You, and I have entrusted my affair to You, and I have leaned my back upon 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." Then if he dies, he dies upon the natural disposition (fitrah).