Mark 9:28-29

9:28 Then, ¹  after he went into the house, his disciples asked him privately, “Why couldn’t we cast it out?” 9:29 He told them, “This kind can come out only by prayer.” ² 

[9:28]  ¹ tn Here καί (kai) has been translated as “then” to indicate the implied sequence of events within the narrative.

[9:29]  ² tc Most witnesses, even early and excellent ones (Ì^45vid א² A C D L W Θ Ψ Ë^1,13 33 Ï lat co), have “and fasting” (καὶ νηστείᾳ, kai nhsteia) after “prayer” here. But this seems to be a motivated reading, due to the early church’s emphasis on fasting (TCGNT 85; cf., e.g., 2 Clem. 16:4; Pol. Phil 7:2; Did. 1:3; 7:4). That the most important witnesses (א* B), as well as a few others (0274 2427 k), lack καὶ νηστείᾳ, when a good reason for the omission is difficult to find, argues strongly for the shorter reading.