Kural - 267

The hotter glows the fining fire, the gold the brighter shines;
The pain of penitence, like fire, the soul of man refines

Explanation
Just as gold is purified as heated in the fire, will those shine, who have endured the burning of pain (in frequent austerities).

Tamil Transliteration
Sutachchutarum Ponpol Olivitum Thunpanjjch
Utachchuta Norkir Pavarkku.