Mark 9:17-19

And someone from the crowd answered him, “Teacher, I brought my son to you, for he has a spirit that makes him mute. And whenever it seizes him, it throws him down, and he foams and grinds his teeth and becomes rigid. So I asked your disciples to cast it out, and they were not able.” And he answered them, “O faithless generation, how long am I to be with you? How long am I to bear with you? Bring him to me.”