Deuteronomy 19:4-7

4And this is the case of the slayer, who shall flee there, that he may live: Whoever killeth his neighbour unintentionally, whom he hated not in time past;1

5As when a man goeth into the forest with his neighbour to hew wood, and his hand maketh a stroke with the axe to cut down the tree, and the head slippeth from the helve, and falleth upon his neighbour, that he dieth; he shall flee to one of these cities, and live:234

6Lest the avenger of blood shall pursue the slayer, while his heart is hot, and overtake him, because the way is long, and slay him; though he was not worthy of death, inasmuch as he hated him not in time past.56

7Therefore I command thee, saying, Thou shalt set apart three cities for thee.