Numbers 35:6-8

6“Now among the cities which you will give to the Levites you shall appoint six cities of refuge, to which a manslayer may flee. And to these you shall add forty-two cities.

7So all the cities you will give to the Levites shall be forty-eight; these you shall give with their common-land.

8And the cities which you will give shall be from the possession of the children of Israel; from the larger tribe you shall give many, from the smaller you shall give few. Each shall give some of its cities to the Levites, in proportion to the inheritance that each receives.”