Whatever you may fail to guard, guard well your tongue, For flawed speech unfailingly invokes anguish and affliction.
By a single word of injury Do all a man's virtues lose their goodness.
The wound caused by fire heals in its time; The burn inflicted by an inflamed tongue never heals.
Tirukkural 13: 126-129
The pen may be mightier than the sword but the tongue beats them all.