The Levites: David: Made Them Attend in Courses
Source: TTT
2 Chronicles 8:14
In keeping with the ordinances of his father David, Solomon appointed the divisions of the priests over their service, and the Levites for their duties to offer praise and to minister before the priests according to the daily requirement. He also appointed gatekeepers by their divisions at each gate, for this had been the command of David, the man of God.
2 Chronicles 31:17
and to the priests enrolled according to their families in the genealogy, as well as to the Levites twenty years of age or older, according to their duties and divisions.