Numbers 35:6-15

And among the cities which ye shall give unto the Levites there shall be six cities for refuge, which ye shall appoint for the manslayer, that he may flee thither: and to them ye shall add forty and two cities. So all the cities which ye shall give to the Levites shall be forty and eight cities: them shall ye give with their suburbs. And the cities which ye shall give shall be of the possession of the children of Israel: from them that have many ye shall give many; but from them that have few ye shall give few: every one shall give of his cities unto the Levites according to his inheritance which he inheriteth. And the LORD spake unto Moses, saying, Speak unto the children of Israel, and say unto them, When ye be come over Jordan into the land of Canaan; then ye shall appoint you cities to be cities of refuge for you; that the slayer may flee thither, which killeth any person at unawares. And they shall be unto you cities for refuge from the avenger; that the manslayer die not, until he stand before the congregation in judgment. And of these cities which ye shall give six cities shall ye have for refuge. Ye shall give three cities on this side Jordan, and three cities shall ye give in the land of Canaan, which shall be cities of refuge. These six cities shall be a refuge, both for the children of Israel, and for the stranger, and for the sojourner among them: that every one that killeth any person unawares may flee thither.