It is better to keep silent than to open one's mouth and remove all doubt.
It is better to remain silent and be thought a fool, than to open your mouth and remove all doubt . -- George Eliot
Better to remain silent and be thought a fool than to speak out and remove all doubt.-- Abraham Lincoln (also attr. Confucius)
It is better to keep your mouth closed and let people think you are a fool than to open it and remove all doubt.-- Mark Twain (1835-1910)
Even a fool, when he holdeth his peace, is counted wise: and he that shutteth his lips is esteemed a man of understanding. -- Bible, 'Proverbs' 17:28.