Numbers 3:38-39

38Moses, Aaron, and Aaron’s sons were to camp to the east of the tabernacle, toward the sunrise, before the Tent of Meeting. They were to perform the duties of the sanctuary as a service on behalf of the Israelites; but any outsider who approached the sanctuary was to be put to death.

39The total number of Levites that Moses and Aaron counted by their clans at the LORD’s command, including all the males a month old or more, was 22,000.