Authentic Supplication Number 30.

When the Prophet of Allah  wanted to sleep he would put his right hand under his cheek and then would say: ‘Allahumma qinee `athabaka yawma tab`athu `ibadaka (51).

Footnotes.
(51) O’ Allah save me from your torment on the Day when You shall resurrect your bondservants.

Reporters.
Reported by Abu Dawood, and At-Tirmithi who said it was comely-sound. Al-Albani agreed, and he included it in The Authentic of Good Sayings as #30.