Numbers 7:6-9

6So Moses took the carts and oxen and gave them to the Levites. 7He gave the Gershonites two carts and four oxen, as their service required, 8and he gave the Merarites four carts and eight oxen, as their service required, all under the direction of Ithamar son of Aaron the priest. 9But he did not give any to the Kohathites, since they were to carry on their shoulders the holy objects for which they were responsible.