Mark 9:16-18

9:16 He asked them, “What are you arguing about with them?” 9:17 A member of the crowd said to him, “Teacher, I brought you my son, who is possessed by a spirit that makes him mute. 9:18 Whenever it seizes him, it throws him down, and he foams at the mouth, grinds his teeth, and becomes rigid. I asked your disciples to cast it out, but ¹  they were not able to do so.” ² 

[9:18]  ¹ tn Here καί (kai) has been translated as “but” to indicate the contrast present in this context.

[9:18]  ² tn The words “to do so” are not in the Greek text, but have been supplied for clarity and stylistic reasons.