1 Corinthians 10:16, 21

The cup we use in the Lord's Supper and for which we give thanks to God: when we drink from it, we are sharing in the blood of Christ. And the bread we break: when we eat it, we are sharing in the body of Christ.

You cannot drink from the Lord's cup and also from the cup of demons; you cannot eat at the Lord's table and also at the table of demons.