Rashi on Numbers 18:6/רש"י על במדבר י״ח:ו׳

1לכם מתנה נתתים TO YOU THEY ARE GIVEN AS A GIFT — I might think that they are given unto you for your private work! It, however, states, “[to you they are given as a gift] for the Lord” — meaning, as explained above (v. 2), — to keep the charge of Temple treasuries and superintendents (Sifrei Bamidbar 116:2).