Deuteronomy 19:5

5as when a person goes into the forest with his friend to cut wood, and his hand 19:5 Lit is put to theswings the axe to cut down the tree, and the iron head slips off the 19:5 Lit woodhandle and 19:5 Lit findsstrikes his friend so that he dies—he may flee to one of these cities and live.