You shall not murder. You shall not commit adultery. You shall not steal. You shall not bear false witness against your neighbor.

(1) To not testify falsely: To not testify [with] false testimony, as it states (Exodus 20:13), “You shall not bear false witness against your neighbor.” And it is repeated in another place in another negative commandment — the “vain witness.”

(3) The laws of the commandment — for example, from whom do we accept testimony (Mishneh Torah, Laws of Testimony 9:1) and from whom do we not accept [it]; what is it that disqualifies people from testifying; how is [the process] of accepting testimony; that there are people that do not testify for anyone, due to their great stature; examination of the testimony and the interrogation; the differences between testimony in financial cases and capital cases; the difference between investigation and corroboration; the difference between [written] testimony and oral; and the rest of its many details are elucidated in Sanhedrin and in [other places] in the Gemara. (See Tur, Choshen Mishpat 38.)

Do not accept a false report.

(1) To not hear the claim of a litigant when it is not in front of his fellow litigant: That the judge not hear the claim of one, not in front of his adversary, as it is stated (Exodus 23:1), “You shall not raise a false report.” And the reason is because people will speak idle words when not in front of their adversary. And the judge is commanded about this so that he not bring the untruths of one of them into his soul. And so does Mekhilta DeRabbi Yishmael 23:1 come [to tell us] that this warning of “You shall not raise, etc.” is said about this. And they also said there that it is also a warning to the litigant, for him too, not to make his claims to the judge not in front of his adversary, and even if the judge wants to hear it. And about this, it is also said (Exodus 23:7), “From a false matter, distance yourself.” And they, may their memory be blessed, also said (Makkot 23a) that this negative commandment includes telling evil speech, and accepting it, and giving false testimony.

(2) The root of this commandment is revealed, as falsehood is “disgraceful and vile” in the eye of any intelligent one; also because the world stands upon true testimony, since all [types] of arguments can be [settled by] the testimony of people. And, if so, false testimony is a cause for the destruction of the world.

(2) The root of this commandment is well-known, as falsehood is abominable and vile in the eyes of all. There is nothing more disgusting than it, and malediction and curse are in the house of its lovers. [This is] because God, may He be blessed, is a truthful God, and everything that is with Him is true. And blessing is only found and resting upon those who model themselves after Him in their deeds: to be truthful, like He is truthful; to be merciful, like He is merciful; and to be purveyors of kindness, like He is of great kindness. But [regarding] anyone whose deeds are the opposite of His good traits and are masters of falsehood — which is exactly the opposite of His traits — the opposite of His traits will similarly always rest upon them. And the opposite of the trait of blessing which is with Him is malediction and curse; and the opposite of joy and peace and enjoyment which are with Him is worry, strife and pain. All of these are the “evildoer’s portion from God.” And therefore the Torah warned us to distance ourselves much from falsehood, as it is written, “From a false matter, distance yourself,” And behold, it used an expression of distancing, due to it being very disgusting; something it did not mention in all the other warnings. And from the side of distancing, it warned us not to bend our ears at all to anything that is considered falsehood — and even if we do not know with certainty that it is a false matter. And [this is] similar to what they, may their memory be blessed, said (Chullin 44b), “Distance yourself from what is ugly, and from what is similar to it.” And in my saying, “the traits of the Holy One, blessed be He,” I am pulled after the words of our Rabbis, may their memory be blessed, who related to Him, may He be blessed, the name of traits according to the side of those receiving them (people). But to Him, may He be blessed, from His side — in His greatness and His uniqueness — one cannot ascribe traits. As He and His wisdom and His will and His power and His traits are [all] one, without any combination or division in the world.

And we have been obligated about the fences of truth because [truth] is from the foundations of the soul.

(181) The fourth section: One who lies in recounting things that he heard and alters some of them on purpose, yet he does not have any benefit from his lies, nor does he cause a loss to anyone else... And they permitted this section in order to fulfill a commandment and to seek good and peace. And they said (Ketuvot 17a) that it is permissible to praise the bride in front of the groom and to say that she is fair and attractive, even though it is not so. And they said (Yevamot 65b) [that] it is permissible to alter [the truth] for matters of peace.

Rav Yehuda says that Shmuel says: With regard to these three matters alone, it is normal for Sages to amend their statements and deviate from the truth: With regard to a tractate, if he is asked whether he studied a particular tractate, he may humbly say that he did not, even if he did. And with regard to a bed, if someone asks you whether you had relations with your spouse. Answer him, “No.” This is the character trait of modesty, and with regard to hospitality [ushpiza], when people ask you whether your host treated you well. Answer them, “No.” This is a good character trait to prevent undesirable guests from returning repeatedly, inundating the host and ultimately exhausting his resources. [Note: this is not a case of lashon hara, prohibited derogatory information, since one is protecting the host from harmful, undesirable guests, Tosafos, ibid., s.v. b’ushpizah.]