Mark 9:18
And wheresoever he taketh him, he teareth him: and he foameth, and gnasheth with his teeth, and pineth away: and I spake to thy disciples that they should cast him out; and they could not.
Cross-reference
Mark 9:20 shows the described symptoms happening — the father's report comes true when the boy is brought to Jesus.
Mark 9:26 shows the same spirit's violent convulsion described in 9:18, fulfilling the father's report.
In Mark 9:28, the disciples privately ask Jesus why they failed — directly continuing this exorcism account.
In Mark 9:29, Jesus says this kind requires prayer — the teaching that follows the failed exorcism here.
In Matthew 17:16, the father tells Jesus the disciples couldn't heal his son — the Matthean parallel to this incident.
In Matthew 17:19-21, Jesus explains the failure was due to little faith — the parallel teaching to this event.
Luke 9:39 gives the same symptoms — seizing, convulsing, foaming — in the parallel account of this boy.
In Luke 9:40, the father reports the disciples' inability — the Lukan parallel to this scene.
In Matthew 17:16, the father tells Jesus the disciples couldn't heal his son — the Matthean parallel to this incident.
In 2 Kings 4:29-31, Gehazi fails to raise a dead boy with Elisha's staff — similar to the disciples' failure here, both require the prophet's direct intervention.