Matthew 13:10
And the disciples came up [and] said to him, "{Why} do you speak to them in parables?"
Mark 4:10
And when he was alone, those around him together with the twelve began asking him about the parables.
Mark 4:33-34
And with many parables such as these he was speaking 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?