2 Chronicles 23:4

This, is the thing that ye shall do, - A third of you entering on the sabbath, both of the priests and of the Levites, as doorkeepers of the porch;

1 Chronicles 9:25

And, their brethren in their villages, had to come in, every seven days, from time to time, along with these.

1 Chronicles 23:3-6

Now the Levites were numbered, from thirty years old and upwards, - and their number by their polls, of mature men, was thirty-eight thousand.

1 Chronicles 24:3-6

and David apportioned to them courses, both to Zadok of the sons of Eleazar, and to Ahimelech of the sons of Ithamar, - by their appointed place in their service.

1 Chronicles 26:13-16

Yea they east lots, as the small so the great, by their ancestral house, for every several gate.

Luke 1:8-9

But it came to pass, as he was doing priestly service in the order of his daily course, before God,

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
Now the Levites were numbered, from thirty years old and upwards, - and their number by their polls, of mature men, was thirty-eight thousand.
1 Chronicles 24:3
and David apportioned to them courses, both to Zadok of the sons of Eleazar, and to Ahimelech of the sons of Ithamar, - by their appointed place in their service.
Luke 1:8
But it came to pass, as he was doing priestly service in the order of his daily course, before God,

Porters

1 Chronicles 26:13
Yea they east lots, as the small so the great, by their ancestral house, for every several gate.