Jesus heals a demon-possessed boy when the disciples lacked enough faith (Matthew 17:14 – 17:23).
When Jesus and the three disciples came to the crowd (presumably returning from atop the mountain where the disciples witnessed the transfiguration), a man approached Jesus and knelt before him. “Lord, have mercy on my son,” he said. “He has seizures and is suffering greatly. He often falls into the fire or into the water.