When the Prophet ﷺ would retire to his bed, he would place his right hand under his cheek and say, "My Lord, protect me from Your punishment on the Day You resurrect," or "gather Your servants."
حدثنا سفيان عن عبد الملك عن ربعي
كان يعني النبي ﷺ إذا أوى إلى فراشه وضع يده اليمنى تحت خده وقال رب يعني قني عذابك يوم تبعث أو تجمع عبادك
Its isnad is sahih, its narrators are trustworthy and well known. Abdul-Malik is the son of Umayr, and Rubai is the son of Harrash. The hadith has previously appeared at 18602.