Joshua 20:3-5

3that the slayer who unwittingly without intent smiteth any one mortally may flee thither: and they shall be your refuge from the avenger of blood.

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

5And if the avenger of blood pursue after him, they shall not deliver the slayer up into his hand; for he smote his neighbour unwittingly, and hated him not previously.