Hadithcore
Mishkat al-Masabih, 2159

He reported the Prophet (ﷺ) as saying, “If anyone who is about to sleep on his bed lies on his right side, then recites ‘Say, He is God, One’ a hundred times, the Lord will say to him on the day of resurrection, ‘My servant, enter paradise to your right’.” Tirmidhī transmitted it, saying this is a <i>hasan gharīb</i> tradition.

وَعَنْ أَنَسٍ عَنِ النَّبِيِّ صَلَّى اللَّهُ عَلَيْهِ وَسَلَّمَ:

مِنْ أَرَادَ أَنْ يَنَامَ عَلَى فِرَاشِهِ فَنَامَ عَلَى يَمِينِهِ ثُمَّ قَرَأَ مِائَةَ مَرَّةٍ (قل هُوَ الله أحد) إِذا كَانَ يَوْم الْقِيَامَةِ يَقُولُ لَهُ الرَّبُّ: يَا عَبْدِي ادْخُلْ عَلَى يَمِينِكَ الْجَنَّةَ

. رَوَاهُ التِّرْمِذِيُّ وَقَالَ: هَذَا حَدِيثٌ حَسَنٌ غَرِيبٌ

References1 variant
In-Book Reference
Book 8, Hadith 49