Mark 9:17-19

17A man in the crowd answered, “Teacher, I brought you my son, who is possessed by a spirit that has robbed him of speech.

18Whenever it seizes him, it throws him to the ground. He foams at the mouth, gnashes his teeth and becomes rigid. I asked your disciples to drive out the spirit, but they could not.”

19“You unbelieving generation,” Jesus replied, “how long shall I stay with you? How long shall I put up with you? Bring the boy to me.”