But I will continue to do what I am doing, in order to deny the opportunity of those who want an opportunity to be regarded just as our equals in what they boast about. For such people are false apostles, deceitful workers, disguising themselves as apostles of Christ. And no wonder! For Satan disguises himself as an angel of light. So it is no great thing if his servants also disguise themselves as servants of righteousness. Their destiny will be according to their works.
2 Corinthians 11:12-15 HCSB
Be on the guard for false prophets, as they have been sent by the devil to deceive you and make you give away your soul! As Jesus has instructed us in the past, test all who come to you by their fruit; for good fruit does not come from a bad limb, and bad fruit does not come from a good limb.
Watch the tongue of those who profess to be Christians; if hatred comes from their mouth, they are not of God, but of the devil.