Rashi on Numbers 1:53/רש"י על במדבר א׳:נ״ג

1ולא יהיה קצף THAT THERE BE NO ANGER [UPON THE CONGREGATION] — If you act according to My commands there will be no anger, but if not, — i.e., that strangers take part in this their (the Levites’) service, there will be anger, just as we find at the incident with Korah (Numbers 17:11): “for there is anger gone forth [from the Lord]”.