Deuteronomy 13:6
If your very own brother, or your son or daughter, or the wife you love, or your closest friend secretly entices you, saying "Let us go worship other gods", do no yield to him or listen to him. Show him no pity. Do not spare him or shield him. You must certain put him to death. Your hand must be the first in putting him to death, and then the hands of all the people. Stone him to death, because he tried to turn you away from the Lord your God, who brought you out of Egypt, out of land of slavery. Then all Israel will hear and be afraid, and no one amoung you will do such evil thing again.
You suppose to kill your brother, son, or daughter, or wife if they worship other Gods.
Edit to add: If you are another Christian apologists who are going to say don't interpret this literally, please spare me. I have heard that too many times. Basically interpret good things from bible literally and not bad things. Give me a break.