2 Chronicles 23:4

This is the thing which ye shall do: a third part of you that come in on the sabbath, of the priests and of the Levites, shall be keepers of the doors;

1 Chronicles 9:25

And their brethren, in their villages, were to come after every seven days from time to time with them.

1 Chronicles 23:3-6

And the Levites were numbered from thirty years old and upward; and their number, by their polls, man by man, was thirty-eight thousand.

1 Chronicles 24:3-6

And David distributed them, both Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, according to their office in their service.

1 Chronicles 26:13-16

And they cast lots, the small as well as the great, according to their fathers' houses, for every gate.

Luke 1:8-9

And it came to pass, as he fulfilled his priestly service before God in the order of his course,

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
And the Levites were numbered from thirty years old and upward; and their number, by their polls, man by man, was thirty-eight thousand.
1 Chronicles 24:3
And David distributed them, both Zadok of the sons of Eleazar, and Ahimelech of the sons of Ithamar, according to their office in their service.
Luke 1:8
And it came to pass, as he fulfilled his priestly service before God in the order of his course,

Porters

1 Chronicles 26:13
And they cast lots, the small as well as the great, according to their fathers' houses, for every gate.