Sahih Bukhari Volume 008, Book 075, Hadith Number 326.

Narated By Hudhaifa : When the Prophet went to bed at night, he would put his hand under his cheek and then say, "Allahumma bismika amutu wa ahya," and when he got up, he would say, "Al-Hamdu lil-lahi al-ladhi ahyana ba'da ma amatana, wa ilaihi an-nushur."