2 Chronicles 31:17

and those who were reckoned by genealogy of the priests by their fathers' houses, and the Levites from twenty years old and upward, in their offices by their divisions;

1 Chronicles 23:24

These were the sons of Levi after their fathers' houses, even the heads of the fathers' houses of those who were counted individually, in the number of names by their polls, who did the work for the service of the house of Yahweh, from twenty years old and upward.

1 Chronicles 23:27

For by the last words of David the sons of Levi were numbered, from twenty years old and upward.

Numbers 3:15

"Count the children of Levi by their fathers' houses, by their families. You shall count every male from a month old and upward."

Numbers 3:20

The sons of Merari by their families: Mahli and Mushi. These are the families of the Levites according to their fathers' houses.

Numbers 4:3

from thirty years old and upward even until fifty years old, all who enter into the service, to do the work in the Tent of Meeting.

Numbers 4:38

Those who were numbered of the sons of Gershon, their families, and by their fathers' houses,

Numbers 4:42

Those who were numbered of the families of the sons of Merari, by their families, by their fathers' houses,

Numbers 4:46

All those who were numbered of the Levites, whom Moses and Aaron and the princes of Israel numbered, by their families, and by their fathers' houses,

Numbers 8:24

"This is that which belongs to the Levites: from twenty-five years old and upward they shall go in to wait on the service in the work of the Tent of Meeting;

Numbers 17:2-3

"Speak to the children of Israel, and take of them rods, one for each fathers' house, of all their princes according to their fathers' houses, twelve rods: write every man's name on his rod.

1 Chronicles 24:20-26

Of the rest of the sons of Levi: of the sons of Amram, Shubael; of the sons of Shubael, Jehdeiah.

2 Chronicles 31:2

Hezekiah appointed the divisions of the priests and the Levites after their divisions, every man according to his service, both the priests and the Levites, for burnt offerings and for peace offerings, to minister, and to give thanks, and to praise in the gates of the camp of Yahweh.

Ezra 2:59

These were those who went up from Tel Melah, Tel Harsha, Cherub, Addan, [and] Immer; but they could not show their fathers' houses, and their seed, whether they were of Israel:

Treasury of Scripture Knowledge

Summary

Both to the genealogy of the priests by the house of their fathers, and the Levites from twenty years old and upward, in their charges by their courses;

Bible References

Genealogy

Numbers 3:15
"Count the children of Levi by their fathers' houses, by their families. You shall count every male from a month old and upward."
Numbers 4:38
Those who were numbered of the sons of Gershon, their families, and by their fathers' houses,
Numbers 17:2
"Speak to the children of Israel, and take of them rods, one for each fathers' house, of all their princes according to their fathers' houses, twelve rods: write every man's name on his rod.
Ezra 2:59
These were those who went up from Tel Melah, Tel Harsha, Cherub, Addan, [and] Immer; but they could not show their fathers' houses, and their seed, whether they were of Israel:

Twenty

Numbers 4:3
from thirty years old and upward even until fifty years old, all who enter into the service, to do the work in the Tent of Meeting.
Numbers 8:24
"This is that which belongs to the Levites: from twenty-five years old and upward they shall go in to wait on the service in the work of the Tent of Meeting;
1 Chronicles 23:24
These were the sons of Levi after their fathers' houses, even the heads of the fathers' houses of those who were counted individually, in the number of names by their polls, who did the work for the service of the house of Yahweh, from twenty years old and upward.

By their courses

2 Chronicles 31:2
Hezekiah appointed the divisions of the priests and the Levites after their divisions, every man according to his service, both the priests and the Levites, for burnt offerings and for peace offerings, to minister, and to give thanks, and to praise in the gates of the camp of Yahweh.
1 Chronicles 24:20
Of the rest of the sons of Levi: of the sons of Amram, Shubael; of the sons of Shubael, Jehdeiah.