Kural - 313

Though unprovoked thy soul malicious foes should sting,
Retaliation wrought inevitable woes will bring

Explanation
In an ascetic inflict suffering even on those who hate him, when he has not done them any evil, it will afterwards give him irretrievable sorrow.

Tamil Transliteration
Seyyaamal Setraarkkum Innaadha Seydhapin
Uyyaa Vizhuman Tharum.