Kural - 199

The men of vision pure, from wildering folly free,
Not e'en in thoughtless hour, speak words of vanity

Explanation
Those wise men who are without faults and are freed from ignorance will not even forgetfully speak things that profit not.

Tamil Transliteration
Poruldheerndha Pochchaandhunj Chollaar Maruldheerndha
Maasaru Kaatchi Yavar.