Hadith 34:51
Sahih (Darussalam)
It was narrated from 'Abdullah that:
whenever the Prophet (saas) went to his bed, he would put his hand - meaning his right hand - beneath his cheek then say: "Allahumma qini 'adhabaka yawm tab'athu - [or: tajma'u] - 'ibadaka (O Allah, save me from Your punishment on the Day when You resurrect - or gather - Your slaves)."
حَدَّثَنَا عَلِيُّ بْنُ مُحَمَّدٍ، حَدَّثَنَا وَكِيعٌ، عَنْ إِسْرَائِيلَ، عَنْ أَبِي إِسْحَاقَ، عَنْ أَبِي عُبَيْدَةَ، عَنْ عَبْدِ اللَّهِ، أَنَّ النَّبِيَّ ـ صلى الله عليه وسلم ـ كَانَ إِذَا أَوَى إِلَى فِرَاشِهِ وَضَعَ يَدَهُ - يَعْنِي الْيُمْنَى - تَحْتَ خَدِّهِ ثُمَّ قَالَ " اللَّهُمَّ قِنِي عَذَابَكَ يَوْمَ تَبْعَثُ - أَوْ تَجْمَعُ - عِبَادَكَ "
Original Reference: Sunan Ibn Majah 3877