1 Chronicles 15:2

15:2 Then David said, “Only the Levites may carry the ark of God, for the Lord chose them to carry the ark of the Lord and to serve before him perpetually.

1 Chronicles 23:31

23:31 and whenever burnt sacrifices were offered to the Lord on the Sabbath and at new moon festivals and assemblies. A designated number were to serve before the Lord regularly in accordance with regulations. ¹ 

[23:31]  ¹ tn Heb “by number according to the manner upon them, regularly before the Lord.”