Don't speak unless you can improve on the silence

स्वायत्तमेकान्तगुणं विधात्रा
विनिर्मितं छादनमज्ञतायाः ।
विशेषतः सर्वविदां समाजे
विभूषणं मौनमपण्डितानाम् ॥

- नीतिशतकम्

The creator has gifted human with a natural cloak to conceal his ignorance, with which he can cover himself at all times, for it is always at hand. Silence is indeed the gifted asset, which serves as a peculiarly befitting ornament for the ignorant, especially in an assembly of scholars.

A silent fool is counted wise.
Don't speak unless you can improve on the silence.