They are all over the Bible.
Deuteronomy 13:1: If there arise among you a prophet, or a dreamer of dreams, and giveth thee a sign or a wonder, 2 And the sign or the wonder come to pass, whereof he spake unto thee, saying, Let us go after other gods, which thou hast not known, and let us serve them; 3 Thou shalt not hearken unto the words of that prophet, or that dreamer of dreams: for the LORD your God proveth you, to know whether ye love the LORD your God with all your heart and with all your soul.
Jeremiah 5:31: The prophets prophesy falsely, and the priests bear rule by their means; and my people love to have it so: and what will ye do in the end thereof?
Ezekiel 22:27: Her princes in the midst thereof are like wolves ravening the prey,/span> to shed blood, and to destroy souls, to get dishonest gain.
Matthew 7:15: Beware of false prophets, which come to you in sheep*s clothing, but inwardly they are ravening wolves.
Matthew 15:14: Let them alone: they be blind leaders of the blind. And if the blind lead the blind, both shall fall into the ditch.
Matthew 24:4: And Jesus answered and said unto them, Take heed that no man deceive you. 5 For many shall come in my name, saying, I am Christ; and shall deceive many. 11 And many false prophets shall rise, and shall deceive many. 24 For there shall arise false Christs, and false prophets, and shall shew great signs and wonders; insomuch that, if it were possible, they shall deceive the very elect.
Mark 13:22: For false Christs and false prophets shall rise, and shall shew signs and wonders, to seduce, if it were possible, even the elect.
Romans 16:17: Now I beseech you, brethren, mark them which cause divisions and offences contrary to the doctrine which ye have learned; and avoid them.
1 Corinthians 5:11: But now I have written unto you not to keep company, if any man that is called a brother be a fornicator, or covetous, or an idolater, or a railer, or a drunkard, or an extortioner; with such an one no not to eat.
2 Thessalonians 3:6: Now we command you, brethren, in the name of our Lord Jesus Christ, that ye withdraw yourselves from every brother that walketh disorderly, and not after the tradition which he received of us.
2 John 1:10: If there come any unto you, and bring not this doctrine, receive him not into your house, neither bid him God speed:
We could go on and on with these warnings because God goes on and on with them.