Numbers 35:29-32

29And this shall be unto you a statute of right throughout your generations in all your dwellings.

30Whoever shall smite a person mortally, at the mouth of witnesses shall the murderer be put to death; but one witness shall not testify against a person to cause him to die.

31And ye shall take no satisfaction for the life of a murderer, who is guilty of death, but he shall certainly be put to death.

32And ye shall take no satisfaction for him that hath fled to the city of his refuge, that he should come again to dwell in the land, until the death of the priest.