Perhaps Scott made it up.
His Chapter xxxi of Rob Roy begins with a verse ostensibly from an otherwise unidentified poem, The Gaulliad.
Google brings up nothing but references to this very page of Scott.
Annoying, because I meant to cite it against those who take too seriously the idea of law of war.
Look it up.
In this chapter, Rob Roy's wife is introduced, a martial commander and an unspeakably bloody harridan exulting in atrocities.