Numbers 3:38-39

38But those who were to camp in front of the tabernacle on the east, in front of the tent of meeting, were Moses, Aaron, and his sons. They were responsible for the needs of the sanctuary and for the needs of the Israelites, but the unauthorized person who approached was to be put to death.

39All who were numbered of the Levites, whom Moses and Aaron numbered by the word of the Lord, according to their families, every male from a month old and upward, were 22,000.