Deuteronomy 19:4-7

“Now this is the case of the manslayer who may flee there and live: when he kills his friend unintentionally, not hating him previously— as when a man goes into the forest with his friend to cut wood, and his hand swings the axe to cut down the tree, and the iron head slips off the handle and strikes his friend so that he dies—he may flee to one of these cities and live; otherwise the avenger of blood might pursue the manslayer in the heat of his anger, and overtake him, because the way is long, and take his life, though he was not deserving of death, since he had not hated him previously. Therefore, I command you, saying, ‘You shall set aside three cities for yourself.’