Mark 9:18 records the disciples' failure to cast out the demon, directly leading to Jesus' teaching on prayer and fasting.

Matthew 17:21 is the synoptic parallel -- the same saying about prayer and fasting for this kind of demon, confirming the teaching across Gospels.

Matthew 12:45 shows the unclean spirit returning with seven worse -- highlighting why prayer/fasting is needed to prevent reoccupation.

Luke 11:26 parallels the returning spirit teaching, reinforcing the necessity of prayer/fasting to avoid a worse state after deliverance.

Daniel 9:3 shows the same combination of prayer and fasting as a disciplined seeking of God, as Jesus teaches for overcoming demons.

Acts 14:23 also pairs prayer and fasting for a spiritual task (appointing elders), mirroring the practice Jesus commands.

Ephesians 6:18 calls for constant prayer in spiritual warfare -- broadening Mark 9:29's specific instruction into a general principle for believers.