Matthew 26:70

‘But he denied before them all, saying, “I do not know what you are saying.” '

Peter told her that he did not know what she was talking about. Luke goes further and indicates that he also said, ‘I know Him not'. He must in fact have said something like that otherwise it would not really have been a denial of Jesus. Here we thus have a typical Matthaean abbreviation. (Possibly his full words were, ‘I don't know what you are saying, I don't know Him'). Matthew commences with an indirect denial because he is in fact trying to demonstrate how Peter's denials actually gradually became worse and worse as his desperation grew.