Deuteronomy 13;6-8 

If your brother, the son of mother, or your son or daughter, of the wife you embrace or your closest friend secretly entices you saying, ‘Let us go and worship other gods’- which neither you nor your fathers have known, and of the gods of the peoples around you, hear you or far from you, from one end of the earth to the other- you must not yield to him or listen to him.  Show him no pity, and do not spare him or shield him