It is a sad thing when men have neither enough intelligence to speak well nor enough sense to hold their tongues.
 
[C’est une grande misère que de n’avoir pas assez d’esprit pour bien parler, ni assez de jugement pour se taire.]

Jean de La Bruyère (1645-1696) French essayist, moralist

The Characters [Les Caractères], ch. 5 “Of Society and Conversation [De la Société et de la Conversation],” § 18 (5.18) (1688) [tr. Van Laun (1885)]
    (Source)

(Source (French)). Alternate translations:

'Tis a sad thing when Men have neither Wit enough to speak well, nor Sense enough to hold their tongues.
[Bullord ed. (1696)]

'Tis a sad thing when Men have neither Wit enough to speak well, nor Judgment enough to hold their Tongues.
[Curll ed. (1713)]

It is a sad Thing when Men have neither Wit to speak well, nor Judgment to hold their Tongues.
[Browne ed. (1752)]

It is a great misfortune to have neither wit enough to talk well nor sense enough to keep silence.
[tr. Stewart (1970)]