Mark 9:25-29

And when Jesus saw that a crowd came running together, he rebuked the unclean spirit, saying to it, “You mute and dumb spirit, I command you, come out of him and never enter him again.” And after crying out and convulsing him terribly, it came out, and the boy was like a corpse, so that most of them said, “He is dead.” But Jesus took him by the hand and lifted him up, and he arose. And when he had entered the house, his disciples asked him privately, “Why could not we cast it out? And he said to them, “This kind cannot be driven out by anything but prayer.” 

In the presence of Yeshu the spirit came out angry, but defeated..

For disciples of Yeshu to cast out such powerful spirits, in addition to believing in him, their praying is definitely needed, and should never be neglected.