Deuteronomy 13:6-9

6“If your brother, the son of your mother, or your son or daughter, or the wife you embrace, or your closest friend secretly entices you, saying, ‘Let’s go and worship other gods’ — which neither you nor your ancestors have known,

7any of the gods of the peoples around you, near you or far from you, from one end of the earth to the other —

8do not yield to him or listen to him. Show him no pity, and do not spare him or shield him.

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