Eyes are windows to the soul.
Medieval European proverb
Apparently, this began as, "The eyes are mirrors of the soul." I went looking for the source of this one, and here is what I found:EYES ARE THE MIRROR (MIRRORS) OF THE SOUL -- "A person's thoughts can be ascertained by looking in his or her eyes. The proverb has been traced back in English to 'Regiment of Life' (1545). But the proverb was known much earlier. Cicero (106-43 B.C.) is quoted as saying, 'Ut imago est animi voltus sic indices oculi' (The face is a picture of the mind as the eyes are its interpreter). The Latin proverbs, 'Vultus est index animi' or 'Oculus animi index,' are usually translated as 'The face is the index of the mind.' The French say, 'Les yeux sont le miroir de l'dme (The eyes are the mirror of the soul). 'The eyes are the window of the soul' is a variant form of the proverb..." From "Random House Dictionary of Popular Proverbs and Sayings" by Gregory Y. Titelman (Random House, New York, 1996)