2 Chronicles 23:4

This is the thing that you shall do: of you priests and Levites who come off duty on the Sabbath, one third shall be gatekeepers

1 Chronicles 9:25

And their kinsmen who were in their villages were obligated to come in every seven days, in turn, to be with these,

1 Chronicles 23:3-6

The Levites, thirty years old and upward, were numbered, and the total was 38,000 men.

1 Chronicles 24:3-6

With the help of Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, David organized them according to the appointed duties in their service.

1 Chronicles 26:13-16

And they cast lots by fathers' houses, small and great alike, for their gates.

Luke 1:8-9

Now while he was serving as priest before God when his division was on duty,

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, thirty years old and upward, were numbered, and the total was 38,000 men.
1 Chronicles 24:3
With the help of Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, David organized them according to the appointed duties in their service.
Luke 1:8
Now while he was serving as priest before God when his division was on duty,

Porters

1 Chronicles 26:13
And they cast lots by fathers' houses, small and great alike, for their gates.

The Holy Bible, English Standard Version® copyright © 2001 by Crossway Bibles, a publishing ministry of Good News Publishers.