Numbers 35:20-23

20And if he thrust at him out of hatred, or hurl at him intentionally, so that he die,

21or from enmity smite him with his hand, so that he die, he that smote him shall certainly be put to death; he is a murderer: the avenger of blood shall put the murderer to death, when he meeteth him. —

22But if he have thrust at him suddenly without enmity, or have cast upon him anything unintentionally,

23or [have smitten him] with any stone wherewith one may die, without seeing him, and have cast it upon him so that he die, and he was not his enemy, neither sought his harm: