Numbers 35:8

5 You shall measure outside of the city for the east side two thousand cubits, and for the south side two thousand cubits, and for the west side two thousand cubits, and for the north side two thousand cubits, the city being in the midst. This shall be to them the suburbs of the cities.

6 The cities which you shall give to the Levites, they shall be the six cities of refuge, which you shall give for the manslayer to flee to: and besides them you shall give forty-two cities.

7 All the cities which you shall give to the Levites shall be forty-eight cities; them [shall you give] with their suburbs.

8 Concerning the cities which you shall give of the possession of the children of Israel, from the many you shall take many; and from the few you shall take few: everyone according to his inheritance which he inherits shall give of his cities to the Levites.

9 Yahweh spoke to Moses, saying,

10 Speak to the children of Israel, and tell them, When you pass over the Jordan into the land of Canaan,

11 then you shall appoint you cities to be cities of refuge for you, that the manslayer who kills any person unwittingly may flee there.