Mark 13:6
[For] many [false teachers] will come, claiming to be me, and saying, 'I am [the Christ] and they will lead many people astray.
Mark 13:22
For false Christs and false prophets will appear and they will perform [miraculous] signs and [supernatural] wonders in order to lead astray [even] the elect, if possible.
Matthew 24:5
For many [false teachers] will come, claiming to be me, and saying, 'I am the Christ [i.e., God's specially chosen one]' and they will lead many people away [from the truth].
Matthew 24:11
And many false prophets will appear and will lead many people away [from the truth].
Matthew 24:23-24
Then if anyone says to you, 'Look, here is Christ,' or 'There [he is],' do not believe him.
John 5:43
I have come in my Father's name [i.e., by His authority] and you do not accept me. If someone else comes in his own name [i.e., by his own authority], you will accept him.
John 8:24
Therefore I said to you that you will die [condemned] in your sins. For unless you believe that I am [the Messiah, who came from above. See verse 23], you will die [condemned] in your sins."
Acts 5:36-39
For [remember that] some time ago Theudas appeared, claiming to be someone [important], and that about four hundred people rallied [to his cause], but he was killed and all his men left him and nothing ever came of it.
1 John 4:1
Loved ones, do not believe [the message of] every spirit [i.e., every person claiming to be a teacher], but test the spirits [i.e., require proof that they and their message are genuine] to see whether they represent God [or not], because many false prophets have begun circulating throughout the world.