Jesus expelled an evil spirit and later explained to the disciples why they had failed to do that.

Mark 9:14-29

14 Jesus and those three disciples returned to where the other disciples were. They saw a large crowd around the other disciples and some men who taught the Jewish laws arguing with them. 15 As soon as the crowd saw Jesus, they were very surprised to see him come. So they ran to him and greeted him. 16 He asked them, “What are you arguing about?” 17 A man in the crowd answered him, “Teacher, I brought my son here in order that you would heal him. There is an evil spirit in him that makes him unable to talk. 18 Whenever the spirit attacks him, it throws him down. He foams at the mouth, he grinds his teeth together, and he becomes stiff. I asked your disciples to expel the spirit, but they were not able to do it.” 19 Jesus replied by saying to those people, “◄I am very disappointed that although you have observed how I help people, you do not believe that you are able to do anything!/Why is it that although you have observed how I help people, you do not believe that you are able to do anything?► [RHQ] ◄I have been with you a long time, and you still cannot do what I do!/How long do I have to be with you before you can do what I do?► [RHQ] Bring the boy to me!” 20 So they brought the boy to Jesus. As soon as the evil spirit saw Jesus, it shook the boy severely, and the boy fell on the ground. He rolled around, and he foamed at the mouth. 21 Jesus asked the boy’s father, “How long has he been like this?” He replied, “This started to happen when he was a child. 22 The spirit does not only do this, but he also often throws him into the fire or into the water in order to kill him. But, pity us and help us, if you can!” 23 Jesus exclaimed to him, “Do not say [RHQ] ‘If you can’, for God/I can do anything for people who believe in him/me!” 24 Immediately the child’s father shouted, “I believe that you can help me, but I do not believe strongly. Help me to believe more strongly!” 25 Because Jesus wanted to heal the boy before the crowd got bigger, he rebuked the evil spirit, saying, “You evil spirit, you who are causing this boy to be deaf and unable to talk! I command you to come out of him and never enter him again!” 26 The evil spirit shouted, it shook the boy violently, and then it left the boy. The boy did not move. He seemed like a dead body. So many of the people there said, “He is dead!” 27 However, Jesus took him by the hand and helped him get up. Then the boy stood up. He was healed! 28 Later, when Jesus and his disciples were alone in a house, one of them asked him, “Why were we not able to expel the evil spirit?” 29 He said to them, “You can expel this kind of evil spirit only by your praying that God will give you the power to do it. There is no other way that you can expel them.”