Kural - 879

Destroy the thorn, while tender point can work thee no offence;
Matured by time, 'twill pierce the hand that plucks it thence

Explanation
A thorny tree should be felled while young, (for) when it is grown it will destroy the hand of the feller.

Tamil Transliteration
Ilaidhaaka Mulmaram Kolka Kalaiyunar
Kaikollum Kaazhththa Itaththu.