Numbers 35:1-3, 9-15, 30-34
The LORD said to Moses in the plains of Moab by the Jordan at Jericho, "Command the people of Israel, that they give to the Levites, from the inheritance of their possession, cities to dwell in; and you shall give to the Levites pasture lands round about the cities. The cities shall be theirs to dwell in, and their pasture lands shall be for their cattle and for their livestock and for all their beasts."
And the LORD said to Moses, "Say to the people of Israel, When you cross the Jordan into the land of Canaan, then you shall select cities to be cities of refuge for you, that the manslayer who kills any person without intent may flee there. The cities shall be for you a refuge from the avenger, that the manslayer may not die until he stands before the congregation for judgment. And the cities which you give shall be your six cities of refuge. You shall give three cities beyond the Jordan, and three cities in the land of Canaan, to be cities of refuge. These six cities shall be for refuge for the people of Israel, and for the stranger and for the sojourner among them, that any one who kills any person without intent may flee there.
"If any one kills a person, the murderer shall be put to death on the evidence of witnesses; but no person shall be put to death on the testimony of one witness. Moreover you shall accept no ransom for the life of a murderer, who is guilty of death; but he shall be put to death. And you shall accept no ransom for him who has fled to his city of refuge, that he may return to dwell in the land before the death of the high priest. You shall not thus pollute the land in which you live; for blood pollutes the land, and no expiation can be made for the land, for the blood that is shed in it, except by the blood of him who shed it. You shall not defile the land in which you live, in the midst of which I dwell; for I the LORD dwell in the midst of the people of Israel."