Rashi on Numbers 4:4/רש"י על במדבר ד׳:ד׳

1קדש הקדשים [THIS SHALL BE THE SERVICE OF THE SONS OF KOHATH] THE קדש הקדשים — i.e., whatever is most holy of them all: the Ark, the table, the candelabrum, the altars, the Partition Veil and the vessels of service.