Supposedly from De Oratore, 78 ("...for women more easily preserve the ancient language unaltered, because, not having experience of the conversation of a multitude of people, they always retain what they originally learned..."), reported in Bartlett's Familiar Quotations, 10th ed. (1919). Compare: "Loveliness / Needs not the foreign aid of ornament, / But is when unadorn'd, adorn'd the most", James Thomson, The Seasons, "Autumn", Line 204https://en.wikiquote.org/wiki/Cicero