As far as we know, at least. I mean, it is just possible that Jesus was followed his every waking moment by a very diligent and accurate stenographer who was sure to record his every utterance. But we have no records of this, and it is not very likely, particularly given the low level of literacy at that time.
I think you have said something like this before: If Jesus was, indeed, God and Christianity was true, it would of utmost importance that we know this.
The importance of answering the question, however, does not lower the evidentiary threshold required to support a particular answer. Regardless of whether Jesus was God, the evidence for us to know that is true simply does not exist.