Mark 9:22-24

22and often it has cast him both into fire and into waters that it might destroy him: but if thou couldst [do] anything, be moved with pity on us, and help us.

23And Jesus said to him, The 'if thou couldst' is [if thou couldst] believe: all things are possible to him that believes.

24And immediately the father of the young child crying out said [with tears], I believe, help mine unbelief.