1 Chronicles 9:25

And he commanded them, saying, “This is the thing that you shall do: one-third of you, who come in on the sabbath and keep watch over the king’s house

These were their assignments for their service when they came in to the house of Yahweh according to the legal judgment rendered to them by the hand of Aaron their father, just as Yahweh, the God of Israel, had commanded him.

“This is the thing which you shall do: one-third of you, of the priests and Levites who come in on the sabbath, shall be gatekeepers at the thresholds,

Now these are the heads of the provinces who lived in Jerusalem, but in the cities of Judah each lived in his own possession in their cities—the Israelites, the priests, the Levites, the temple servants, and the sons of Solomon’s servants.