2 Chronicles 23:4

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,

1 Chronicles 9:25

Their relatives in their villages were to come in every seven days from time to time to be with them;

1 Chronicles 23:3-6

The Levites were numbered from thirty years old and upward, and their number by census of men was 38,000.

1 Chronicles 24:3-6

David, with Zadok of the sons of Eleazar and Ahimelech of the sons of Ithamar, divided them according to their offices for their ministry.

1 Chronicles 26:13-16

They cast lots, the small and the great alike, according to their fathers’ households, for every gate.

Luke 1:8-9

Now it happened that while he was performing his priestly service before God in the appointed order of his division,

Treasury of Scripture Knowledge

Summary

This is the thing that ye shall do; A third part of you entering on the sabbath, of the priests and of the Levites, shall be porters of the doors;

Bible References

Entering

1 Chronicles 23:3
The Levites were numbered from thirty years old and upward, and their number by census of men was 38,000.
1 Chronicles 24:3
David, with Zadok of the sons of Eleazar and Ahimelech of the sons of Ithamar, divided them according to their offices for their ministry.
Luke 1:8
Now it happened that while he was performing his priestly service before God in the appointed order of his division,

Porters

1 Chronicles 26:13
They cast lots, the small and the great alike, according to their fathers’ households, for every gate.