"And what is right speech? Abstaining from lying, from divisive speech, from abusive speech, & from idle chatter: This is called right speech." — SN XLV.8
"Monks, a statement endowed with five factors is well-spoken, not ill-spoken. It is blameless & unfaulted by knowledgeable people. Which five?
"It is spoken at the right time. It is spoken in truth. It is spoken affectionately. It is spoken beneficially. It is spoken with a mind of good-will." — AN V.198
"For the person who transgresses in one thing, I tell you, there is no evil deed that is not to be done. Which one thing? This: telling a deliberate lie." — Iti 25
“我可以告诉你，如果一个人敢犯有一件事，那么就没有什么坏事他不敢做。这是一件什么事呢？就是故意撒谎。” ——《小部 Iti 25》
"And how is one made pure in four ways by verbal action?
"There is the case where a certain person, abandoning false speech, abstains from false speech. When he has been called to a town meeting, a group meeting, a gathering of his relatives, his guild, or of the royalty, if he is asked as a witness, 'Come & tell, good man, what you know': If he doesn't know, he says, 'I don't know.' If he does know, he says, 'I know.' If he hasn't seen, he says, 'I haven't seen.' If he has seen, he says, 'I have seen.' Thus he doesn't consciously tell a lie for his own sake, for the sake of another, or for the sake of any reward. Abandoning false speech, he abstains from false speech. He speaks the truth, holds to the truth, is firm, reliable, no deceiver of the world.
"Abandoning divisive speech he abstains from divisive speech. What he has heard here he does not tell there to break those people apart from these people here. What he has heard there he does not tell here to break these people apart from those people there. Thus reconciling those who have broken apart or cementing those who are united, he loves concord, delights in concord, enjoys concord, speaks things that create concord.
"Abandoning abusive speech, he abstains from abusive speech. He speaks words that are soothing to the ear, that are affectionate, that go to the heart, that are polite, appealing & pleasing to people at large.
"Abandoning idle chatter, he abstains from idle chatter. He speaks in season, speaks what is factual, what is in accordance with the goal, the Dhamma, & the Vinaya. He speaks words worth treasuring, seasonable, reasonable, circumscribed, connected with the goal.
"This is how one is made pure in four ways by verbal action."
— AN X.176
有这种情况：某个人离于谎言、戒绝了谎言。当他被市镇会议、某个组织会议、亲戚的聚会、行会、或者皇族叫去作证并对他说：“来告诉我们你所知道的，善人。” 如果他不知道，他就说“我不知道。” 如果他知道，他就说“我知道。” 如果他不曾看见，他就说“我不曾看见。” 如果他曾经看见，他就说“我曾经看见。” 这样，他不会为了自己或他人、为了得到报酬而故意撒谎。他抛弃了谎言、戒绝了谎言。他说真实语，坚持真实语，坚定，可靠，不欺世人。
"And how is right view the forerunner? One discerns wrong speech as wrong speech, and right speech as right speech. And what is wrong speech? Lying, divisive tale-bearing, abusive speech, & idle chatter. This is wrong speech...
"One tries to abandon wrong speech & to enter into right speech: This is one's right effort. One is mindful to abandon wrong speech & to enter & remain in right speech: This is one's right mindfulness. Thus these three qualities — right view, right effort, & right mindfulness — run & circle around right speech." — MN 117
 "In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial (or: not connected with the goal), unendearing & disagreeable to others, he does not say them.
 "In the case of words that the Tathagata knows to be factual, true, unbeneficial, unendearing & disagreeable to others, he does not say them.
 "In the case of words that the Tathagata knows to be factual, true, beneficial, but unendearing & disagreeable to others, he has a sense of the proper time for saying them.
 "In the case of words that the Tathagata knows to be unfactual, untrue, unbeneficial, but endearing & agreeable to others, he does not say them.
 "In the case of words that the Tathagata knows to be factual, true, unbeneficial, but endearing & agreeable to others, he does not say them.
 "In the case of words that the Tathagata knows to be factual, true, beneficial, and endearing & agreeable to others, he has a sense of the proper time for saying them. Why is that? Because the Tathagata has sympathy for living beings."
— MN 58
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
— Sn III.3
—— 《小部 Sn III.3〉
[The Buddha speaks to his son, Rahula:] "Whenever you want to perform a verbal act, you should reflect on it: 'This verbal act I want to perform — would it lead to self-affliction, to the affliction of others, or to both? Is it an unskillful verbal act, with painful consequences, painful results?' If, on reflection, you know that it would lead to self-affliction, to the affliction of others, or to both; it would be an unskillful verbal act with painful consequences, painful results, then any verbal act of that sort is absolutely unfit for you to do. But if on reflection you know that it would not cause affliction... it would be a skillful verbal action with happy consequences, happy results, then any verbal act of that sort is fit for you to do.
"While you are performing a verbal act, you should reflect on it: 'This verbal act I am doing — is it leading to self-affliction, to the affliction of others, or to both? Is it an unskillful verbal act, with painful consequences, painful results?' If, on reflection, you know that it is leading to self-affliction, to the affliction of others, or to both... you should give it up. But if on reflection you know that it is not... you may continue with it.
"Having performed a verbal act, you should reflect on it... If, on reflection, you know that it led to self-affliction, to the affliction of others, or to both; it was an unskillful verbal act with painful consequences, painful results, then you should confess it, reveal it, lay it open to the Teacher or to a knowledgeable companion in the holy life. Having confessed it... you should exercise restraint in the future. But if on reflection you know that it did not lead to affliction... it was a skillful verbal action with happy consequences, happy results, then you should stay mentally refreshed and joyful, training day and night in skillful mental qualities."
— MN 61
[佛陀对他的儿子罗侯罗说：] 罗喉罗!当你欲以口作业时，则应省察你之口业：“我将作之口业，会危害自己吗？会危害他人吗？会自、他俩害吗？为不善、成苦果、苦报吗？”罗喉罗，如果省察时你知道：我将作之口业，会危害自己，会危害他人，会自、他俩害，为不善、成苦果、苦报，那么你绝对不应该作如此之口业。但是如果省察时你知道: 我将作之口业，不危害自己，不危害他人，不自、他俩害，为善、成乐果、乐报，那么你应作如此之口业。
"Whereas some priests and contemplatives, living off food given in faith, are addicted to talking about lowly topics such as these — talking about kings, robbers, ministers of state; armies, alarms, and battles; food and drink; clothing, furniture, garlands, and scents; relatives; vehicles; villages, towns, cities, the countryside; women and heroes; the gossip of the street and the well; tales of the dead; tales of diversity [philosophical discussions of the past and future], the creation of the world and of the sea, and talk of whether things exist or not — he abstains from talking about lowly topics such as these. This, too, is part of his virtue.
"Whereas some priests and contemplatives, living off food given in faith, are addicted to debates such as these — 'You understand this doctrine and discipline? I'm the one who understands this doctrine and discipline. How could you understand this doctrine and discipline? You're practicing wrongly. I'm practicing rightly. I'm being consistent. You're not. What should be said first you said last. What should be said last you said first. What you took so long to think out has been refuted. Your doctrine has been overthrown. You're defeated. Go and try to salvage your doctrine; extricate yourself if you can!' — he abstains from debates such as these. This, too, is part of his virtue."
— DN 2
"There are these ten topics of [proper] conversation. Which ten? Talk on modesty, on contentment, on seclusion, on non-entanglement, on arousing persistence, on virtue, on concentration, on discernment, on release, and on the knowledge & vision of release. These are the ten topics of conversation. If you were to engage repeatedly in these ten topics of conversation, you would outshine even the sun & moon, so mighty, so powerful — to say nothing of the wanderers of other sects." — AN X.69
有十种[恰当]的话题。哪十种呢？谈论少欲、知足、远离、离缚、精进、戒、定、慧、解脱、解脱知见。这就是十种[恰当]的话题。如果你常常参与这十种对话，你甚至会比巨大而俱大力之日月更光耀，更不用说别的宗教的修行人。 ——《增支部 X.69》
"O bhikkhus, a bhikkhu who desires to admonish another should do so after investigating five conditions in himself and after establishing five other conditions in himself. What are the five conditions which he should investigate in himself?
 "Am I one who practices purity in bodily action, flawless and untainted...?
 "Am I one who practices purity in speech, flawless and untainted...?
 "Is the heart of goodwill, free from malice, established in me towards fellow-farers in the holy life...?
 "Am I or am I not one who has heard much, who bears in mind what he has heard, who stores up what he has heard? Those teachings which are good alike in their beginning, middle, and ending, proclaiming perfectly the spirit and the letter of the utterly purified holy life — have such teachings been much heard by me, borne in mind, practiced in speech, pondered in the heart and rightly penetrated by insight...?
 "Are the Patimokkhas [rules of conduct for monks and nuns] in full thoroughly learned by heart, well-analyzed with thorough knowledge of their meanings, clearly divided sutta by sutta and known in minute detail by me...?
"These five conditions must be investigated in himself.
"And what other five conditions must be established in himself?
 "Do I speak at the right time, or not?
 "Do I speak of facts, or not?
 "Do I speak gently or harshly?
 "Do I speak profitable words or not?
 "Do I speak with a kindly heart, or inwardly malicious?
"O bhikkhus, these five conditions are to be investigated in himself and the latter five established in himself by a bhikkhu who desires to admonish another."
— AN V (From The Patimokkha, Ñanamoli Thera, trans.)