1 Chronicles 16:37

So he left there before the ark of the covenant of the LORD Asaph and his brethren to minister before the ark continually, each thing in its day;

2 Chronicles 8:14

And he appointed, according to the order of David his father, the courses of the priests to their service and the Levites to their charges, to praise and minister before the priests, each thing in its day; the porters also by their courses at each gate, for so had David, the man of God, commanded.

Ezra 3:4

They kept also the feast of the tabernacles, as it is written, and offered the daily burnt offerings by number, according to the ordinance, each thing in its day,

1 Chronicles 15:17-24

So the Levites appointed Heman, the son of Joel; and of his brethren, Asaph, the son of Berechiah; and of the sons of Merari and of their brethren, Ethan the son of Kushaiah,

1 Chronicles 16:4-6

And he appointed certain of the Levites to minister before the ark of the LORD and to record and to thank and praise the LORD God of Israel:

1 Chronicles 25:1-6

Moreover David and the captains of the host separated unto the ministry the sons of Asaph and of Heman and of Jeduthun, who should prophesy with harps, with psalteries, and with cymbals; and the number of men that were suitable for the work of their respective ministry was,

Treasury of Scripture Knowledge

Summary

So he left there before the ark of the covenant of the LORD Asaph and his brethren, to minister before the ark continually, as every day's work required:

Bible References

Before the ark

1 Chronicles 16:4
And he appointed certain of the Levites to minister before the ark of the LORD and to record and to thank and praise the LORD God of Israel:
1 Chronicles 15:17
So the Levites appointed Heman, the son of Joel; and of his brethren, Asaph, the son of Berechiah; and of the sons of Merari and of their brethren, Ethan the son of Kushaiah,
1 Chronicles 25:1
Moreover David and the captains of the host separated unto the ministry the sons of Asaph and of Heman and of Jeduthun, who should prophesy with harps, with psalteries, and with cymbals; and the number of men that were suitable for the work of their respective ministry was,

As every

2 Chronicles 8:14
And he appointed, according to the order of David his father, the courses of the priests to their service and the Levites to their charges, to praise and minister before the priests, each thing in its day; the porters also by their courses at each gate, for so had David, the man of God, commanded.
Ezra 3:4
They kept also the feast of the tabernacles, as it is written, and offered the daily burnt offerings by number, according to the ordinance, each thing in its day,