Numbers 3:38-39

38Moreover those who were to camp before the tabernacle on the east, before the tabernacle of meeting, were Moses, Aaron, and his sons, keeping charge of the sanctuary, to meet the needs of the children of Israel; but the outsider who came near was to be put to death.

39All who were numbered of the Levites, whom Moses and Aaron numbered at the commandment of the Lord, by their families, all the males from a month old and above, were twenty-two thousand.