It’s better to keep your mouth shut and appear stupid, than to open it and remove all doubt.

Mark Twain (1835-1910) American writer [pseud. of Samuel Clemens]

(Spurious)

This quotation, and close variants, are frequently attributed to Twain or Abraham Lincoln, but appears to have first been phrased this way by Maurice Switzer, Mrs. Goose, Her Book (1906):

It is better to remain silent at the risk of being thought a fool, than to talk and remove all doubt of it.

Another point of origin is in the Bible, Proverbs 17:28:

Even a fool, when he holdeth his peace, is counted wise: and he that shutteth his lips is esteemed a man of understanding.

In short, the sentiment is not new. See also See also Fuller, Franklin, Thomas a Kempis, and Wilson. For more discussion, see:

• Quote Origin: Better to Remain Silent and Be Thought a Fool than to Speak and Remove All Doubt – Quote Investigator®
• Keep Your Mouth Shut And Appear Stupid Quote | Quotationize