Numbers 3:39-41

New Revised Standard Version, Anglicised Catholic Edition

³⁹ The total enrolment of the Levites whom Moses and Aaron enrolled at the commandment of the Lord, by their clans, all the males from a month old and upwards, was twenty-two thousand.

The Redemption of the Firstborn

⁴⁰ Then the Lord said to Moses: Enrol all the firstborn males of the Israelites, from a month old and upwards, and count their names. ⁴¹ But you shall accept the Levites for me—I am the Lord—as substitutes for all the firstborn among the Israelites, and the livestock of the Levites as substitutes for all the firstborn among the livestock of the Israelites.