General Behavior (Kitab Al-Adab)

Dawud :: Book 41 : Hadith 5027

Narrated Hafsah, Ummul Mu'minin:

When the Apostle of Allah (peace_be_upon_him) 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.