Musnad Abu Ya'la al-Mawsili 210:3

Ibrahim ibn al-Hajjaj al-Sami narrated to us, Hammad narrated to us, from Asim ibn Bahdalah, from Suwa, from Hafsa, the wife of the Prophet, may God bless him and grant him peace: That the Prophet, may God bless him and grant him peace, when he would retire to his bed, he would lie on his right side and say: "My Lord, protect me from Your punishment on the day You resurrect Your servants."