Numbers 35:14-24

14 Ye shall give three cities on this side of the Jordan, and three cities shall ye give in the land of Canaan, which shall be cities of refuge.
15 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 who killeth any person unawares may flee thither.
16 "`And if he smite him with an instrument of iron so that he die, he is a murderer: the murderer shall surely be put to death.
17 And if he smite him with throwing a stone wherewith he may die, and he die, he is a murderer: the murderer shall surely be put to death.
18 Or if he smite him with a hand weapon of wood wherewith he may die, and he die, he is a murderer: the murderer shall surely be put to death.
19 The avenger of blood himself shall slay the murderer; when he meeteth him, he shall slay him.
20 But if he thrust him out of hatred, or hurl at him by lying in wait so that he die,
21 or in enmity smite him with his hand so that he die, he that smote him shall surely be put to death, for he is a murderer: the avenger of blood shall slay the murderer when he meeteth him.
22 "`But if he thrust him suddenly without enmity, or have cast upon him anything without lying in wait,
23 or with any stone wherewith a man may die, seeing him not and casting it upon him so that he die, and was not his enemy neither sought his harm,
24 then the congregation shall judge between the slayer and the avenger of blood according to these judgments.