Sahih Bukhari Volume 008, Book 075, Hadith Number 323.
Narated By Al-Bara bin 'Azib : Allah's Apostle said to me, "When you want to go to bed, perform ablution as you do for prayer, then lie down on your right side and say: 'Allahumma aslamtu wajhi ilaika, wa fauwadtu Amri ilaika wa aljatu zahri ilaika, raghbatan wa rahbatan ilaika, lamalja'a wa la manja mink a ill a ilaika. Amantu bikitabi kalladhi anzalta wa bi nabiyyikal-ladhi arsalta'. If you should die then (after reciting this) you will die on the religion of Islam (i.e., as a Muslim); so let these words be the last you say (before going to bed)" While I was memorizing it, I said, "Wa birasiulikal-ladhi arsalta (in Your Apostle whom You have sent).' The Prophet said, "No, but say: Wa binabiyyi-kalladhi arsalta (in Your Prophet whom You have sent)."