Deuteronomy 19:4-6

JPS_ASV_Byz(i) 4 And this is the case of the manslayer, that shall flee thither and live: whoso killeth his neighbour unawares, and hated him not in time past; 5 as when a man goeth into the forest with his neighbour to hew wood, and his hand fetcheth a stroke with the axe to cut down the tree, and the head slippeth from the helve, and lighteth upon his neighbour, that he die; he shall flee unto one of these cities and live; 6 lest the avenger of blood pursue the manslayer, while his heart is hot, and overtake him, because the way is long, and smite him mortally; whereas he was not deserving of death, inasmuch as he hated him not in time past.