Joshua 20:3-5

3That the slayer that killeth any person unintentionally and unknowingly may flee there: and they shall be your refuge from the avenger of blood.

4And when he that doth flee to one of those cities shall stand at the entrance of the gate of the city, and shall declare his cause in the ears of the elders of that city, they shall take him into the city to them, and give him a place, that he may dwell among them.

5And if the avenger of blood shall pursue him, then they shall not deliver the slayer into his hand; because he smote his neighbour unknowingly, and had not hated him in times past.