Numbers 3:4

3:4 Nadab and Abihu died before the Lord when they offered strange fire before the Lord in the wilderness of Sinai, and they had no children. So Eleazar and Ithamar ministered as priests in the presence of Aaron their father.

Numbers 4:28

4:28 This is the service of the families of the Gershonites concerning the tent of meeting. Their responsibilities will be under the authority of Ithamar son of Aaron the priest.