Matthew 13:10
And the disciples came and said to him, Why do you say things to them in the form of stories?
Mark 4:10
And when he was by himself, those who were round him with the twelve put questions to him about the purpose of the stories.
Mark 4:33-34
And with a number of such stories he gave them his teaching, as they were able to take it:
Treasury of Scripture Knowledge
Summary
And the disciples came, and said unto him, Why speakest thou unto them in parables?