First, let me say this. None of the Gospels that chronicle Jesus' life were witnessed by the authors. Mark--written between 65-70 AD. Matthew--written between 70-100 AD. Luke--written between 80-100 AD. John--written between 90-100 AD. And, the four Gospels differ depending on the emphasis the writer intended.
The stories of Christ were first handed down verbally. That means that the writers had to rely on word of mouth depictions of events and words.
So, even the writers of the time can be accused of putting words into Jesus' mouth that he didn't say.
This is in no way to refute any of the Bible, nor anything else. This is just reality. Try recounting a conversation, word for word, five minutes after with another it is over. Most people can't do it.