Thirukkural

அழச்சொல்லி அல்லது இடித்து வழக்கறிய வல்லார்நடபு ஆய்ந்து கொளல்.

Azhachcholli Alladhu Itiththu Vazhakkariya Vallaarnatapu Aaindhu Kolal

You should examine and secure the friendship of those who can speak so as to make you weep over a crime (before its commission) or rebuke you severely (after you have done it) and are able to teach