When the Prophet ﷺ would sleep, he would put his hand under his head then say: “O Allah, safeguard me from Your Punishment the Day You gather [Your slaves] (Allāhumma qinī ʿadhābaka yawma tajmaʿu [ʿibādak])” or “you resurrect your slaves (tabʿathu ʿibādak).”  

أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا أَرَادَ أَنْ يَنَامَ وَضَعَ يَدَهُ تَحْتَ رَأْسِهِ ثُمَّ قَالَ اللَّهُمَّ قِنِي عَذَابَكَ يَوْمَ تَجْمَعُ عِبَادَكَ أَوْ تَبْعَثُ عِبَادَكَ قَالَ هَذَا حَدِيثٌ حَسَنٌ صَحِيحٌ  

The Messenger of Allah ﷺ used to lay his head upon his right hand when going to sleep, then say: “My Lord, safeguard me from Your punishment the Day You resurrect Your slaves (Rabbi qinī ʿadhābaka yawma tabʿathu ʿibādak).”  

كَانَ رَسُولُ اللَّهِ ﷺ يَتَوَسَّدُ يَمِينَهُ عِنْدَ الْمَنَامِ ثُمَّ يَقُولُ رَبِّ قِنِي عَذَابَكَ يَوْمَ تَبْعَثُ عِبَادَكَ