Idolatry: Saints should not Have Religious Intercourse with Those Who Practise
Source: TTT
Joshua 23:7
So you are not to associate with these nations that remain among you. You must not call on the names of their gods or swear by them, and you must not serve them or bow down to them.
1 Corinthians 5:11
But now I am writing you not to associate with anyone who claims to be a brother but is sexually immoral or greedy, an idolater or a verbal abuser, a drunkard or a swindler. With such a man do not even eat.