Musnad Ahmad 26:676

Waki' narrated to us, from Isra'il, from Abu Ishaq, from Abu 'Ubaydah, from 'Abdullah, that the Prophet, peace and blessings of Allah be upon him, when he would go to his bed, he would place his hand under his cheek and say: "O Allah, protect me from Your punishment on the day You resurrect Your servants."