I have heard that on one occasion the Blessed One was staying in Savatthi at Jeta's Grove, Anathapindika's park. There he addressed the monks, "Monks!"
"Yes, lord," the monks replied.
The Blessed One said: "Monks, speech endowed with four characteristics is well-spoken, not poorly spoken -- faultless & not to be faulted by the wise. Which four? There is the case where a monk says only what it well-spoken, not what is poorly spoken; only what is just, not what is unjust; only what is endearing, not what is un-endearing; only what is true, not what is false. Speech endowed with these four characteristics is well-spoken, not poorly spoken -- faultless & not to be faulted by the wise."
That is what the Blessed One said. Having said this, the One Well-Gone, the Teacher, said further:
The calm say that what is well-spoken is best;
second, that one should say
what is just, not unjust;
third, what is endearing, not un-endearing;
fourth, what is true, not false.
Then Ven. Vangisa, rising from his seat, arranging his robe over one shoulder, faced the Blessed One with his hands palm-to-palm in front of his heart and said, "An inspiration has come to me, Blessed One! An inspiration has come to me, One Well-Gone!"
"Let the inspiration come to you, Vangisa," the Blessed One said.
Then Ven. Vangisa praised the Blessed One to his face with these attractive verses:
Speak only the speech
that neither torments self
nor does harm to others.
That speech is truly well spoken.
Speak only endearing speech,
speech that is welcomed.
Speech when it brings no evil
to others is pleasant.
Truth, indeed, is deathless speech:
This is an ancient principle.
The goal and the Dhamma
-- so say the calm --
are firmly established on truth.
The speech the Awakened One speaks,
for attaining Unbinding,
for making an end
to the mass of stress:
That is the speech unexcelled.