It is narrated from Sayyiduna Rafi' (may Allah be pleased with him) that the Prophet (peace and blessings be upon him) said: "When one of you lies down on his right side and then says: O Allah, I have surrendered myself to You, entrusted my back to Your protection, and handed over my affair to You; there is no place of refuge from You except towards You; and, O our Lord, I believe in You and in Your messengers - then if he dies that very night, he will enter Paradise."
Hadith Referenceالمعجم الكبير للطبراني / باب الراء / 4405