Numbers 4:37-39

New Catholic Bible

³⁷ This was the number of those in the families of the Kohathites who ministered in the tent of meeting, whom Moses and Aaron counted, fulfilling the commandment of the Lord given to Moses.

³⁸ The sons of Gershon were counted by families and clan ³⁹ counting those who were from thirty years old to fifty years old and who went in to minister in the service of the tent of meeting.