Sunan Ibn Majah 3877
سنن ابن ماجه#3877SahihIt 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)
Scholarly Authentication
We show the most cautious grade (weakest-wins) as the overall label. Individual scholars graded it as follows:
Al-AlbaniSahih
Muhammad Fouad Abd al-BaqiSahih
Zubair Ali ZaiSahih
In-book reference: 34:51