Howell, James -- Paroimiographia [Παροιμιογραφία]: Proverbs, or, Old Sayed Sawes & Adages, “Proverbs in Italian” (1659) [compiler]

By seeing one thou knowest him half, by hearing him speak thou knowst all. [Vedendo uno conosci mezzo, udendolo parlar il conosci tutto.] See also the Bible, Menander.