Messenger of Allah (ﷺ) directed me thus: "Whenever you go to bed, perform Wudu' as you do for Salat then (before sleeping) recite: 'O Allah! I have submitted myself to You, I have turned myself to You, committed my affairs to You and sought Your refuge for protection out of desire for You and fear of You (expecting Your reward and fearing Your punishment). There is no refuge and no place of safety from You but with You. I believe in the Book You have revealed and in the Prophet (ﷺ) You have sent."' Messenger of Allah (ﷺ) added: "If anyone recites these words and dies during the night, he will die on the true Deen, and if he remains alive till the morning, he will obtain good. And make this supplication your last words (before sleeping)."

[Al-Bukhari and Muslim].