Numbers 35:6-8

35:6 Now from these towns that you will give to the Levites you must select six towns of refuge to which a person who has killed someone may flee. And you must give them forty-two other towns.

35:7 “So the total of the towns you will give the Levites is forty-eight. You must give these together with their grazing lands. 35:8 The towns you will give must be from the possession of the Israelites. From the larger tribes you must give more; and from the smaller tribes fewer. Each must contribute some of its own towns to the Levites in proportion to the inheritance allocated to each.