Mt. 17:14-21; Mk. 9:14-29; Lk. 9:37-43
The next day after the transfiguration, Jesus and the three disciples came down from the mountain and found the scribes in a deep discussion with the other nine disciples. One man in the multitude had a son who was afflicted with epileptic seizures and the disciples had been unable to heal the boy. After Jesus had removed the demon, the people were amazed at the majesty of God.
Jesus pointed out to the disciples that their faith was not strong enough to perform this miracle. Even if they had the faith of a mustard seed, they could move mountains.