બોલે નહીં તે બોળી મારે, તે કાળજું કારે.

bōlē nahīṁ tē bōḷī mārē, tē kāḷajuṁ kārē.

Literally: He who does not speak strikes silently, that pierces the heart.
What it means: Silent people are often the most dangerous because their intentions are hidden.
The English proverb Shah set beside it: Silent men and still waters are deep and dangerous.Beware of a silent dog and still waters.

Also said as

ગુજરાતી કહેવતસંગ્રહ (Gujarati Kahevat Sangrah) (1923) · read from the scan by machine — the Gujarati itself is unchecked · English is machine-made and nobody has checked it yet

Heard it differently, or know we've got the sense wrong? Tell us — that is exactly the kind of correction this needs.