The Prophet (sal-Allaahu 'alayhe wa sallam) would place his right hand under his cheek when about to sleep and supplicate:
اللَّهُمَّ قِنِي عَذَابَكَ يَوْمَ تَبْعَثُ عِبَادَكَ
O Allaah, protect me from Your punishment on the day Your servants are resurrected.'
Allaahumma qinee 'athaabaka yawma tab'athu 'ibaadaka.
Abu Dawud 4/311, Sahih At-Tirmizi 3/143.