Matthew 13:10
Then the disciples came and said to him, "Why do you speak to them in parables?"
Mark 4:10
And when he was alone, those around him with the twelve asked him about the parables.
Mark 4:33-34
With many such parables he spoke the word to them, as they were able to hear it.
Treasury of Scripture Knowledge
Summary
And the disciples came, and said unto him, Why speakest thou unto them in parables?