Ezekiel 40:46

40:46 and the chamber which faces north is for the priests who keep charge of the altar. These are the descendants of Zadok, from the descendants of Levi, who may approach the Lord to minister to him.”

Leviticus 10:3

10:3 Moses then said to Aaron, “This is what the Lord spoke: ‘Among the ones close to me I will show myself holy, and in the presence of all the people I will be honored.’” So Aaron kept silent.

Numbers 16:5

16:5 Then he said to Korah and to all his company, “In the morning the Lord will make known who are his, and who is holy. He will cause that person to approach him; the person he has chosen he will cause to approach him.

Numbers 16:40

16:40 It was a memorial for the Israelites, that no outsider who is not a descendant of Aaron should approach to burn incense before the Lord, that he might not become like Korah and his company – just as the Lord had spoken by the authority of Moses.

Numbers 18:7

18:7 But you and your sons with you are responsible for your priestly duties, for everything at the altar and within the curtain. And you must serve. I give you the priesthood as a gift for service; but the unauthorized person who approaches must be put to death.”

Deuteronomy 21:5

21:5 Then the Levitical priests will approach (for the Lord your God has chosen them to serve him and to pronounce blessings in his name, and to decide every judicial verdict)