It is narrated from Sayyidah Hafsah bint Umar (may Allah be pleased with her) that when the Messenger of Allah (peace and blessings be upon him) intended to sleep, he would place his right hand under his right cheek and then say: "O Allah, protect me from Your punishment on the Day You resurrect Your servants."
Hadith Referenceالمعجم الكبير للطبراني / مسند النساء / 19698