Numbers 35:14 (KJV)

And the LORD spake unto Moses, saying,

Speak unto the children of Israel, and say unto them, When ye be come over Jordan into the land of Canaan;

Then ye shall appoint you cities to be cities of refuge for you; that the slayer may flee thither, which killeth any person at unawares.

And they shall be unto you cities for refuge from the avenger; that the manslayer die not, until he stand before the congregation in judgment.

And of these cities which ye shall give six cities shall ye have for 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.

Or if he smite him with an hand weapon of wood, 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.