Kural - 826

Though many goodly words they speak in friendly tone,
The words of foes will speedily be known

Explanation
Though (one's) foes may utter good things as though they were friends, once will at once understand (their evil, import).

Tamil Transliteration
Nattaarpol Nallavai Sollinum Ottaarsol
Ollai Unarap Patum.