Numbers 35:6-15

[Among] the cities which you give to the Levites shall be the six cities of refuge, which you shall provide for the one who commits manslaughter to flee to; and in addition to them you shall give forty-two cities [to the Levites]. So you shall give to the Levites forty-eight cities in all, together with their pasture lands. As for the cities which you shall give from the possession of the Israelites, from the larger tribes you shall take many and from the smaller tribes few; each tribe shall give [at least some] of its cities to the Levites in proportion to [the size of] its inheritance which it possesses.” Then the LORD spoke to Moses, saying, “Tell the Israelites, ‘When you cross the Jordan [River] into the land of Canaan, then you shall select for yourselves cities to be cities of refuge, so that the one who kills any person unintentionally may escape there. The cities shall be to you as a refuge from the avenger, so that the one who has caused the death of another will not be killed until he has had a [fair] trial before the congregation. The cities which you are to provide shall be your six cities of refuge. You shall provide three cities on this [east] side of the Jordan [River], and three [more] cities in the land of Canaan; they are to be the cities of refuge. These six cities shall be a refuge for the Israelites and for the stranger and the resident alien among them; so that anyone who kills a person unintentionally may escape there.