19 then came the disciples to Jesus in private, and said, why could not we cast him out?
Matthew 17:19 Cross References - Mace
Mark 4:10
10 And when he was in private, the twelve, and some of his disciples asked him the meaning of the parable.
Mark 9:28
28 now when Jesus was retired to his own house, his disciples asked him in private, why could not we cast this spirit out?