This Bible contradiction is from the Skeptic's Annotated Bible.
Matthew 13:10-11 View context
And the disciples came, and said unto him, Why speakest thou unto them in parables?
He answered and said unto them, Because it is given unto you to know the mysteries of the kingdom of heaven, but to them it is not given.
Mark 4:10-11 View context
And when he was alone, they that were about him with the twelve asked of him the parable.
And he said unto them, Unto you it is given to know the mystery of the kingdom of God: but unto them that are without, all [these] things are done in parables:
Luke 8:9-10 View context
And his disciples asked him, saying, What might this parable be?
And he said, Unto you it is given to know the mysteries of the kingdom of God: but to others in parables; that seeing they might not see, and hearing they might not understand.
John 18:20 View context
Jesus answered him, I spake openly to the world; I ever taught in the synagogue, and in the temple, whither the Jews always resort; and in secret have I said nothing.