Kural - 34

Spotless be thou in mind! This only merits virtue's name;
All else, mere pomp of idle sound, no real worth can claim

Explanation
Let him who does virtuous deeds be of spotless mind; to that extent is virtue; all else is vain show.

Tamil Transliteration
Manaththukkan Maasilan Aadhal Anaiththu Aran
Aakula Neera Pira.