Have more than thou showest, Speak less than thou knowest, Lend less than thou owest.
Wise men say nothing in dangerous times
It is a great misfortune neither to have enough wit to talk well nor enough judgment to be silent.
If the prudence of reserve and decorum dictates silence in some circumstances, in others prudence of a higher order may justify us in speaking our thoughts.
The whole art of life is knowing the right time to say things.
Washington once advised his adopted grandson that where there is no occasion for expressing an opinion, it is best to be silent. For there is nothing more certain than that it is at all times more easy to make enemies than friends.
Think twice before you speak, and then you may be able to say something more insulting than if you spoke right out at once.
It is wise to be silent when occasion requires, and better than to speak, though never so well.
Knowing when to say something and when not to say something is important.
If thou desire to be held wise, be so wise as to hold thy tongue.