Numbers 18:2-12

2 So bring with you also your brothers of the tribe of Levi, your ancestral tribe, in order that they may be joined to you, and serve you while you and your sons with you are in front of the tent of the covenant.
3 They shall perform duties for you and for the whole tent. But they must not approach either the utensils of the sanctuary or the altar, otherwise both they and you will die.
4 They are attached to you in order to perform the duties of the tent of meeting, for all the service of the tent; no outsider shall approach you.
5 You yourselves shall perform the duties of the sanctuary and the duties of the altar, so that wrath may never again come upon the Israelites.
6 It is I who now take your brother Levites from among the Israelites; they are now yours as a gift, dedicated to the Lord, to perform the service of the tent of meeting.
7 But you and your sons with you shall diligently perform your priestly duties in all that concerns the altar and the area behind the curtain. I give your priesthood as a gift; any outsider who approaches shall be put to death.
8 The Lord spoke to Aaron: I have given you charge of the offerings made to me, all the holy gifts of the Israelites; I have given them to you and your sons as a priestly portion due you in perpetuity.
9 This shall be yours from the most holy things, reserved from the fire: every offering of theirs that they render to me as a most holy thing, whether grain offering, sin offering, or guilt offering, shall belong to you and your sons.
10 As a most holy thing you shall eat it; every male may eat it; it shall be holy to you.
11 This also is yours: I have given to you, together with your sons and daughters, as a perpetual due, whatever is set aside from the gifts of all the elevation offerings of the Israelites; everyone who is clean in your house may eat them.
12 All the best of the oil and all the best of the wine and of the grain, the choice produce that they give to the Lord, I have given to you.