Sahih Bukhari
Oneness, Uniqueness of Allah (Tawheed)
Volume: 009 / Book Number: 093 / Hadith Number: 490
Narrated Abu Huraira:
The Prophet said, "When anyone of you goes to bed, he should dust it off thrice with the edge of his garment, and say: Bismika Rabbi wada'tu janbi, wa bika arfa'hu. In amsakta nafsi faghfir laha, wa in arsaltaha fahfazha bima tahfaz bihi 'ibadaka-s-salihin."