Numbers 35:6-8

Six of the cities you give the Levites are to be appointed as cities of refuge, to which a manslayer may flee. In addition to these, give the Levites forty-two other cities.

The total number of cities you give the Levites will be forty-eight, with their corresponding pasturelands.

The cities that you apportion from the territory of the Israelites should be given to the Levites in proportion to the inheritance of each tribe: more from a larger tribe and less from a smaller one.”