Mark 9:16-19

He asked them, “What are you discussing with them?” One of the crowd replied to Him, “Teacher, I brought You my son, possessed with a spirit which makes him unable to speak; and whenever it seizes him [intending to do harm], it throws him down, and he foams [at the mouth], and grinds his teeth and becomes stiff. I told Your disciples to drive it out, and they could not do it.” He replied, “O unbelieving (faithless) generation, how long shall I be with you? How long shall I put up with you? Bring him to Me!”