Kural - 127

Whate'er they fail to guard, o'er lips men guard should keep;
If not, through fault of tongue, they bitter tears shall weep

Explanation
Whatever besides you leave unguarded, guard your tongue; otherwise errors of speech and the consequent misery will ensue.

Tamil Transliteration
Yaakaavaa Raayinum Naakaakka Kaavaakkaal
Sokaappar Sollizhukkup Pattu.