Kural - 133

'Decorum's' true nobility on earth;
'Indecorum's' issue is ignoble birth

Explanation
Propriety of conduct is true greatness of birth, and impropriety will sink into a mean birth.

Tamil Transliteration
Ozhukkam Utaimai Kutimai Izhukkam
Izhindha Pirappaai Vitum.