Al-Bara' said, "When the Prophet, may Allah bless him and grant him peace, wanted to go to sleep, he put his hand under his right cheek and said, 'O Allah, protect me from Your punishment on the Day you raise up Your slaves.'"
كَانَ النَّبِيُّ ﷺ إِذَا أَرَادَ أَنْ يَنَامَ وَضَعَ يَدَهُ تَحْتَ خَدِّهِ الأَيْمَنِ وَيَقُولُ اللَّهُمَّ قِنِي عَذَابَكَ يَوْمَ تَبْعَثُ عِبَادَكَ
When the Messenger of Allah ﷺ wanted to go to sleep, he put his right hand under his cheek and would then say three times: O Allah, guard me from Thy punishment on the day when Thou raisest up Thy servants.
عَنْ حَفْصَةَ زَوْجِ النَّبِيِّ ﷺ أَنَّ رَسُولَ اللَّهِ ﷺ كَانَ إِذَا أَرَادَ أَنْ يَرْقُدَ وَضَعَ يَدَهُ الْيُمْنَى تَحْتَ خَدِّهِ ثُمَّ يَقُولُ اللَّهُمَّ قِنِي عَذَابَكَ يَوْمَ تَبْعَثُ عِبَادَكَ ثَلاَثَ مِرَارٍ
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
that whenever the Prophet ﷺ went to bed, he would put his right hand underneath his cheek and then say, "O Allah, save me from Your punishment on the Day when You resurrect" or "gather Your slaves."
أَنَّ النَّبِيَّ ﷺ كَانَ إِذَا أَوَى إِلَى فِرَاشِهِ وَضَعَ يَدَهُ يَعْنِي الْيُمْنَى تَحْتَ خَدِّهِ ثُمَّ قَالَ: «اللَّهُمَّ قِنِي عَذَابَكَ يَوْمَ تَبْعَثُ» أَوْ «تَجْمَعُ عِبَادَكَ۔»