Numbers 35:13-17

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.