Numbers 3:38-39

38Now those to camp before the tabernacle toward the east, before the Tent of Meeting, toward the sunrise, were to be Moses, and Aaron and his sons, performing the duties of the sanctuary for whatever was required of the Israelites; and the layman (non-Levite) who approached [the sanctuary] was to be put to death.

39All the men of the Levites whom Moses and Aaron numbered at the command of the Lord, by their families, every male from a month old and upward, were 22,000.