Albert Barnes on John 18:32

That the saying of Jesus, &c. To wit, that he would be delivered into the hands of the Gentiles and be crucified, Mt 20:19. Neither of these things would have happened if he had been put to death in the way that the Jews first contemplated, Mt 26:4. Though it should be admitted that they had the power, in religious cases, to do this, yet in such a case it would not have been done, as Jesus predicted, by the Gentiles; and even if it should be admitted that they had the right to take life, yet they had not the right to do it by crucifixion. This was particularly a Roman punishment. And thus it was ordered, in the providence of God, that the prediction of Jesus in both these respects was fulfilled.

(v) "That the saying of Jesus" Mt 20:19, Lk 18:32,33