The phrase "rest in peace" typically occurs on (headstones), often abbreviated "RIP." "Rest in peace" is a prayer that the deceased may
rest peacefully, not in
torment, while awaiting
Judgment Day. The expression comes originally from "requiescat in pace", Latin for "may he rest in peace." In Italian, it is said as "Riposi In Pace."
See more at Wikipedia.org...
Let him/her rest in peace. (May he/she rest in peace)