Mencius - Book 4, Part 1, Chapter 15

Mencius said, 'Of all the parts of a man's body there is none more excellent than the pupil of the eye. The pupil cannot be used to hide a man's wickedness. If within the breast all be correct, the pupil is bright. If within the breast all be not correct, the pupil is dull.

'Listen to a man's words and look at the pupil of his eye. How can a man conceal his character?'
~ James Legge translation via nothingistic.org ~

Go here to read the introductory post to this serialized version of the Works of Mencius.