Sahih Bukhari: Hadith 6089

That the Prophet (ﷺ) advised a man, saying, "If you intend to lie down (i.e. go to bed), say, 'Allahumma aslamtu nafsi ilaika wa fauwadtu `Amri ilaika, wa wajjahtu wajhi ilaika wa alja'tu zahri ilaika, reghbatan wa rahbatan ilaika. La malja'a wa la manja minka illa ilaika. Amantu bikitabikal-ladhi anzalta; wa nabiyyikalladhi arsalta.' And if you should die then (after reciting this before going to bed) you will die on the religion of Islam"