Tirukkural-On Virtue-Avoiding Idle Talk-Kural 197

Add as a preferred source on Google

Men of virtue too may sometimes speak unfairly;It were better, that they do not talk uselessly.

This Kural would imply that idle talk is more productive of evil than even unjust words. That is why, in delineating the virtues of a 'Sanron', Valluvar might admit of this virtuous man lapsing sometimes into unfair speech but never into idle talk.