Mark 14:71
He began to call down curses, and he swore to them, I don't know this man you're talking about — the third denial is the most emphatic: cursing (possibly calling curses on himself if he is lying) and swearing (invoking God as witness). The escalation from I don't know to I don't understand to I don't know this man communicates the progressive depth of the denial. This man is as far as Peter can get from the you are the Messiah declaration of 8:29.