Sanhedrin 83 - Transgressions and Punishments of a Kohen
Rav Acha bur Huna inquired of Rav Sheshet, "If a Kohen served in the Temple in a state of spiritual impurity, is he liable to death at the hands of Heaven?"
Said Rav Sheshet, "You answer is in the previous ruling : young Kohanim remove him outside the Courtyard and split open his skull with clubs. If he is liable at the hands of Heaven, simply leave him to die at the hands of Heaven!" Answered Rav Acha, "But could it be that he is not liable at the hands of Heaven, and yet we we kill him?" The final rule is that the Kohen is indeed liable to death at the hands of Heaven, but only if he performed a concluding service.
The following are liable to death at the hands of Heaven: one who eats produce before tithe separation, a non-Kohen who eats a Kohen's portion, a non-Kohen who serves in the Temple, and a ritually impure Kohen who serves in the Temple.
Art: Le Nain Brothers- The Peasant Meal