Sahih Bukhari Volume 008, Book 075, Hadith Number 332.

Narated By Abu Huraira : The Prophet said, "When anyone of you go to bed, he should shake out his bed with the inside of his waist sheet, for he does not know what has come on to it after him, and then he should say: 'Bismika Rabbi wada'tu Janbi wa bika arfa'uhu, In amsakta nafsi farhamha wa in arsaltaha fahfazha bima tahfazu bihi ibadakas-salihin."