Celsus continues: “The disciples of Jesus, having no undoubted fact on which to rely, devised the fiction that he foreknew everything before it happened;” not observing, or not wishing to observe, the love of truth which actuated the writers, who acknowledged that Jesus had told His disciples beforehand, “All you shall be offended because of Me this night,”— a statement which was fulfilled by their all being offended; and that He predicted to Peter, “Before the cock crow, you shall deny Me thrice,” which was followed by Peter's threefold denial.
Now if they had not been lovers of truth, but, as Celsus supposes, inventors of fictions, they would not have represented Peter as denying, nor His disciples as being offended. For although these events actually happened, who could have proved that they turned out in that manner? And yet, according to all probability, these were matters which ought to have been passed over in silence by men who wished to teach the readers of the Gospels to despise death for the sake of confessing Christianity. But now, seeing that the word, by its power, will gain the mastery over men, they related those facts which they have done, and which, I know not how, were neither to do any harm to their readers, nor to afford any pretext for denial.
Source: Against Celsus (New Advent)