sleep of the just

noun2

1. •
   A deep and worry-free sleep.

   • Make your mind easy, Percival. Sleep, my son, the sleep of the just; and see what I will do for you when daylight comes to help us both. — 1859
2. •
   (euphemistic, old-fashioned) A peaceful death or burial.

   • At length he [Jean-Pierre-François Guillot-Duhamel] slept the sleep of the just, on the 19th February 1816, aged somewhat less than 86 years old. — 1830