“It is wise to be silent when occasion requires, and better than to speak, though never so well.”
Moralia, Of the Training of Children
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Plutarch 251
ancient Greek historian and philosopher 46–127Related quotes

“621. Speake fitly, or be silent wisely.”
Jacula Prudentum (1651)

“The Wise are silent, the Foolish speak, and children are thus led astray.”

“There are occasions when it pays better to fight and be beaten than not to fight at all.”
Charles Dickens (1939)
Source: Homage to Catalonia

Source: The Cabinet Council (published 1658), Chapter 25

“I am never silent. I speak eternally.”
"I Speak Eternally" http://www.avatarmeherbaba.org/erics/ispeak.html in Love Alone Prevails (1981) by Kitty Davy, p. 166, 179.
General sources
Context: External silence helps to achieve inner Silence, and only in internal Silence is Baba found — in profound inner Silence. I am never silent. I speak eternally. The voice that is heard deep within the soul is My voice — the voice of inspiration, of intuition, of guidance. Through those who are receptive to this voice, I speak.