Deuteronomy 13:6-9

6If your very own brother, or your son or daughter, or the wife you embrace,1 or your closest friend secretly entices you, saying, “Let us go and worship other gods” (which neither you nor your fathers have known, 7the gods of the peoples around you, whether near or far, whether from one end of the earth or the other), 8you must not yield to him or listen to him. Show him no pity, and do not spare him or shield him.

9Instead, you must surely kill him. Your hand must be the first against him to put him to death, and then the hands of all the people.