Teachings on truthfulness

KN Iti 25, makes the same point as MN 61, that lying leads to every other kind of evil

♦ “eka-dhammaṃ atītassa, bhikkhave, purisa-puggalassa
“one-thing transgressed, *********, (for a) person,
nāhaṃ tassa kiñci pāpa-kammaṃ a-karaṇīyanti
there is no evil-action not-(to be)-done.
vadāmi.
(this I) say.
katamaṃ eka-dhammaṃ?
Which one thing?
yadidaṃ bhikkhave, sampajāna-musā-vādo”ti.
just-this, monks: deliberate-lie-telling."
etam-atthaṃ bhagavā avoca.
this-(is the)-meaning (of what) the-blessed-one said.
tatth-etaṃ iti vuccati —
(with regard to)-that thus (was it) said.
(verse)
♦ “eka-dhammaṃ atītassa,
"one-thing transgressed,
musā-vādissa jantuno.
lying-speech (by a) person,
♦ vitiṇṇa-para-lokassa,
rejecting-[concern for the]-after-world,
natthi pāpaṃ a-kāriyan”ti.
(there is)-no evil (he will) not-do."

“Further, he reflects thus: ‘If someone were to damage my well-being by telling a lie, that would be displeasing & disagreeable to me. And if I were to damage the well-being of another by telling a lie, that would be displeasing & disagreeable to the other. What is displeasing & disagreeable to me is displeasing & disagreeable to others. How can I inflict on others what is displeasing & disagreeable to me?’ Reflecting in this way, he himself refrains from telling lies, he gets others to refrain from telling lies, and he speaks in praise of refraining from telling lies. In this way, his verbal behavior is pure in three ways."

~ the Buddha, Veḷudvāreyya Sutta: The People of Bamboo Gate, transl. Thanissaro https://www.dhammatalks.org/suttas/SN/SN55_7.html

MN 114 expands on this some.

‘I say that there are two kinds of verbal behavior: that which you should cultivate, and that which you should not cultivate. And each of these is a kind of verbal behavior.’ That’s what the Buddha said, but why did he say it? You should not cultivate the kind of verbal behavior which causes unskillful qualities to grow while skillful qualities decline. And you should cultivate the kind of verbal behavior which causes unskillful qualities to decline while skillful qualities grow.

And what kind of verbal behavior causes unskillful qualities to grow while skillful qualities decline? It’s when someone lies. They’re summoned to a council, an assembly, a family meeting, a guild, or to the royal court, and asked to bear witness: ‘Please, mister, say what you know.’ Not knowing, they say ‘I know.’ Knowing, they say ‘I don’t know.’ Not seeing, they say ‘I see.’ And seeing, they say ‘I don’t see.’ So they deliberately lie for the sake of themselves or another, or for some trivial worldly reason. They speak divisively. They repeat in one place what they heard in another so as to divide people against each other. And so they divide those who are harmonious, supporting division, delighting in division, loving division, speaking words that promote division. They speak harshly. They use the kinds of words that are cruel, nasty, hurtful, offensive, bordering on anger, not leading to immersion. They talk nonsense. Their speech is untimely, and is neither factual nor beneficial. It has nothing to do with the teaching or the training. Their words have no value, and are untimely, unreasonable, rambling, and pointless. That kind of verbal behavior causes unskillful qualities to grow while skillful qualities decline.

And what kind of verbal behavior causes unskillful qualities to decline while skillful qualities grow? It’s when a certain person gives up lying. They’re summoned to a council, an assembly, a family meeting, a guild, or to the royal court, and asked to bear witness: ‘Please, mister, say what you know.’ Not knowing, they say ‘I don’t know.’ Knowing, they say ‘I know.’ Not seeing, they say ‘I don’t see.’ And seeing, they say ‘I see.’ So they don’t deliberately lie for the sake of themselves or another, or for some trivial worldly reason. They give up divisive speech. They don’t repeat in one place what they heard in another so as to divide people against each other. Instead, they reconcile those who are divided, supporting unity, delighting in harmony, loving harmony, speaking words that promote harmony. They give up harsh speech. They speak in a way that’s mellow, pleasing to the ear, lovely, going to the heart, polite, likable and agreeable to the people. They give up talking nonsense. Their words are timely, true, and meaningful, in line with the teaching and training. They say things at the right time which are valuable, reasonable, succinct, and beneficial. That kind of verbal behavior causes unskillful qualities to decline while skillful qualities grow. ‘I say that there are two kinds of verbal behavior: that which you should cultivate, and that which you should not cultivate. And each of these is a kin