They assigned the priests to their divisions and the Levites to their divisions, over the service of God in Jerusalem, as it is written in the Book of Moses.
Ezra 6:18
Surrounding context
6:17 And they offered sacrifices at the dedication of this house of God, one hundred bulls, two hundred rams, four hundred lambs, and as a sin offering for all Israel twelve male goats, according to the number of the tribes of Israel.
6:18 They assigned the priests to their divisions and the Levites to their divisions, over the service of God in Jerusalem, as it is written in the Book of Moses.
6:19 And the descendants of the captivity kept the Passover on the fourteenth day of the first month.