Kural - 958

If lack of love appear in those who bear some goodly name,
'Twill make men doubt the ancestry they claim

Explanation
If one of a good family betrays want of affection, his descent from it will be called in question.

Tamil Transliteration
Nalaththinkan Naarinmai Thondrin Avanaik
Kulaththinkan Aiyap Patum.