Rashi on Numbers 18:23/רש"י על במדבר י״ח:כ״ג

1והם [BUT THE LEVITES SHALL PERFORM THE SERVICE OF THE APPOINTED TENT] AND THEY SHALL BEAR THEIR INIQUITY — “They” means the Levites; they shall bear the iniquity of the children of Israel, because upon them (the Levites) lies the duty to warn them (the Israelites) not to come near unto them.