Matthew 17:9-13

And as they were going down the mountain, Jesus commanded them, “Do not tell anyone what you have seen until the Son of Man has been raised from the dead.” The disciples asked Him, “Then why do the scribes say that Elijah must come first?” He answered and said, “Elijah is coming and will restore all things; but I say to you that Elijah has come already, and they did not recognize him, but did to him as they wished. The Son of Man is also going to suffer at their hands.” Then the disciples understood that He had spoken to them about John the Baptist. [Mal 4:5]