משנה אויף במדבר 17:28

If one steals the sacred vessel called a “kasvah” (Numbers 4:7), or cursed by the name of an idol, or has sexual relations with an Aramean (non-Jewish) woman, he is punished by zealots. If a priest performed the temple service while impure, his fellow priests do not bring him to the court, but rather the young priests take him out into the courtyard and split his skull with clubs. A layman who performed the service in the Temple: Rabbi Akiva says: “He is strangled.” But the Sages say: “[His death is] at the hands of heaven.”