Numbers 3:40

All that were numbered of the Levites, which Moses and Aaron numbered at the commandment of the LORD, throughout their families, all the males from a month old and upward, were twenty and two thousand.

And thou shalt take the Levites for me (I am the LORD) instead of all the firstborn among the children of Israel; and the cattle of the Levites instead of all the firstlings among the cattle of the children of Israel.