The disciples asked him, “Why then do the teachers of the law say that Elijah must come first?”
Jesus replied, “To be sure, Elijah comes and will restore all things.
References for Matthew 17:11
But I tell you, Elijah has already come, and they did not recognize him, but have done to him everything they wished. In the same way the Son of Man is going to suffer at their hands.”
References for Matthew 17:12
Then the disciples understood that he was talking to them about John the Baptist.
References for Matthew 17:13