Sahih Bukhari Volume 008, Book 075, Hadith Number 337.

Narated By Abu Dhar : Whenever the Prophet lay on his bed, he used to say: "Allahumma bismika amutu wa ahya," and when he woke up he would say: "Al-hamdu lil-lahilladhi ahyana ba'da ma an atana, wa ilaihi an-nushur."