2 Corinthians 11:13-15
For such men are false apostles; they are deceitful workers, who disguise themselves as [true] apostles of Christ.
Galatians 2:4
For [certain] false brothers, who were secretly brought in to observe us practicing our liberty in Christ Jesus [i.e., by not having Titus circumcised], attempted to place us [back] under the bondage [of Mosaic law keeping].
2 Timothy 3:8
These people oppose the truth just like Jannes and Jambres opposed Moses. They have corrupt minds and are worthless as far as the faith is concerned.
2 Peter 2:1-2
But just as there were false prophets among the people before, there will also be false teachers among you [Christians]. They will privately teach harmful doctrines that destroy people [spiritually], by even denying [that Jesus is] the Master, [and thereby] destroying themselves quickly.