Numbers 35:18 (KJV)

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.

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.

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.

The revenger of blood himself shall slay the murderer: when he meeteth him, he shall slay him.

But if he thrust him of hatred, or hurl at him by laying of wait, that he die;

Or in enmity smite him with his hand, that he die: he that smote him shall surely be put to death; for he is a murderer: the revenger of blood shall slay the murderer, when he meeteth him.

But if he thrust him suddenly without enmity, or have cast upon him any thing without laying of wait,

Or with any stone, wherewith a man may die, seeing him not, and cast it upon him, that he die, and was not his enemy, neither sought his harm: