Numbers 35:22-23

35:22 “But if he strikes him suddenly, without enmity, or throws anything at him unintentionally, 35:23 or with any stone large enough that a man could die, without seeing him, and throws it at him, and he dies, even though he was not his enemy nor sought his harm,

Exodus 21:13

21:13 But if he does not do it with premeditation, but it happens by accident, then I will appoint for you a place where he may flee.

Deuteronomy 4:42

4:42 Anyone who accidentally killed someone without hating him at the time of the accident could flee to one of those cities and be safe.

Deuteronomy 19:4-5

19:4 Now this is the law pertaining to one who flees there in order to live, if he has accidentally killed another without hating him at the time of the accident. 19:5 Suppose he goes with someone else to the forest to cut wood and when he raises the ax to cut the tree, the ax head flies loose from the handle and strikes his fellow worker so hard that he dies. The person responsible may then flee to one of these cities to save himself.