Numbers 35:19-21

19The avenger of blood himself shall put the murderer to death; when he meets him, he shall put him to death.

20If he pushes him out of hatred or, while lying in wait, hurls something at him so that he dies,

21or in enmity he strikes him with his hand so that he dies, the one who struck him shall surely be put to death. He is a murderer. The avenger of blood shall put the murderer to death when he meets him.