There are something supposedly not lawful to utter
2 Cr12:3 And I knew such a man, (whether in the body, or out of the body, I cannot tell: God knoweth;
2 Cr12:4 How that he was caught up into paradise, and heard unspeakable words, which it is not lawful for a man to utter.
Rev 10:3 And when the seven thunders had uttered their voices, I was about to write:
and I heard a voice from heaven saying unto me, Seal up those things which the seven thunders uttered, and write them not .
Regardless of whether he is speaking of John or not, as some differ