Thirukkural

Kural - 641
A tongue that rightly speaks the right is greatest gain,
It stands alone midst goodly things that men obtain.
The possession of that goodness which is called the goodness of speech is (even to others) better than any other goodness.

Kural - 642
Since gain and loss in life on speech depend,
From careless slip in speech thyself defend.
Since (both) wealth and evil result from (their) speech, ministers should most carefully guard themselves against faultiness therein.

Kural - 643
'Tis speech that spell-bound holds the listening ear,
While those who have not heard desire to hear.
The (minister's) speech is that which seeks (to express) elements as bind his friends (to himself) and is so delivered as to make even his enemies desire (his friendship).

Kural - 644
Speak words adapted well to various hearers' state;
No higher virtue lives, no gain more surely great.
Understand the qualities (of your hearers) and (then) make your speech; for superior to it, there is neither virtue nor wealth.

Kural - 645
Speak out your speech, when once 'tis past dispute
That none can utter speech that shall your speech refute.
Deliver your speech, after assuring yourself that no counter speech can defeat your own.

Kural - 646
Charming each hearer's ear, of others' words to seize the sense,
Is method wise of men of spotless excellence.
It is the opinion of those who are free from defects in diplomacy that the minister should speak so as to make his hearers desire (to hear more) and grasp the meaning of what he hears himself.

Kural - 647
Mighty in word, of unforgetful mind, of fearless speech,
'Tis hard for hostile power such man to overreach.
It is impossible for any one to conquer him by intrique who possesses power of speech, and is neither faulty nor timid.

Kural - 648
Swiftly the listening world will gather round,
When men of mighty speech the weighty theme propound.
If there be those who can speak on various subjects in their proper order and in a pleasing manner, the world would readily accept them.

Kural - 649
Who have not skill ten faultless words to utter plain,
Their tongues will itch with thousand words man's ears to pain.
They will desire to utter many words, who do not know how to speak a few faultless ones.

Kural - 650
Like scentless flower in blooming garland bound
Are men who can't their lore acquired to other's ears expound.
Those who are unable to set forth their acquirements (before others) are like flowers blossoming in a cluster and yet without fragrance.