Deuteronomy 19:4-5

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