Abu Dawud Book 36, Hadith Number 5027.
Chapter : Not known.
Narated By Hafsah, Ummul Mu’minin : When the Apostle of Allah (PBUH) wanted to go to sleep, he put his right hand under his cheek and would then say three times: O Allah, guard me from Thy punishment on the day when Thou raisest up Thy servants.