Galatians 1:8: "But though we, or an angel from heaven, preach any other gospel unto you than that which we have preached unto you, let him be accursed."
See Jeremiah 23:30-32 Jeremiah 23:30: "Therefore, behold, I am against the prophets, saith the LORD, that steal my words every one from his neighbour."

Jeremiah 23:31: "Behold, I am against the prophets, saith the LORD, that use their tongues, and say, He saith."

Jeremiah 23:32: "Behold, I am against them that prophesy false dreams, saith the LORD, and do tell them, and cause my people to err by their lies, and by their lightness; yet I sent them not, nor commanded them: therefore they shall not profit this people at all, saith the LORD." .

Matthew 24:11: "And many false prophets shall rise, and shall deceive many."

Matthew 24:24: "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."