Speech was given to man to conceal his thoughts.

[La parole a été donné à l’homme pour déguiser sa pensée.]

Charles-Maurice de Talleyrand-Périgord (1754-1838) French secularized clergyman, statesman, wit, diplomat

(Attributed)

For more discussion of the sources of this quote, see S. A. Bent, ed., Familiar Short Sayings of Great Men (1887). The sentiment, if not the precise wording, predates Talleyrand.