What does the La'av of "Lo Sisa Sheima Shav" entail?
Rashi #1 (citing Targum Onkelos), R. Bachye #1 (citing the Mechilta) and Targum Yonasan: It is a prohibition against accepting Lashon ha'Ra (or speaking it and against testifying falsely against one's fellow-Jew - Pesachim, 118a). 1 2
Rashi #2 and R. Bachye #2: It is a La'av prohibiting a Dayan from listening to the words of one litigant before his opponent has arrived (and a litigant presenting his claim 3 4 to a judge before his opponent arrives - Sanhedrin, 7b and Mechilta). 5
R. Bachye #3: It is a prohibition against the Dayanim accepting a Shevu'ah from someone whom they suspect will violate it.
Rashbam: It is a La'av prohibiting a Dayan from accepting false testimony - by not thoroughly cross-examining the witnesses 6 and b. a witness from testifying together with false witnesses - even if there are two of them whose testimony will be accepted even without them.
R. Chaim Paltiel: It is a prohibition against the Dayanim accepting a fraudulant claim.
Oznayim la'Torah: Although Onkelos tends to not differentiate between "Shav" and "Sheker", the word "Shav" generally refers to something that is obviously false - in which case the Torah here is forbidding even to listen to Motzi-Shem-Ra which he knows to be untrue and to remain silent, as that only encourages the speaker to continue telling tales about other people.
Pesachim, Ibid.: And the Torah juxtaposes it to "la'Kelev Tashlichun oso" to teach us that anyone who speaks Lashon ha'Ra, accepts Lashon ha'Ra or who testifies falsely against his fellow-Jew deserves to be thrown to the dogs.
Because we read it as if it had written "Lo Sasi" - See Torah Temimah, note 2.
R. Bachye: As Shlomoh ha'Melech wrote in Mishlei 18:17.
Rashbam: See Re'ei Devarim 13:9
What does the La'av of "Al Tasheis Yadcha Im Rasha " entail?
Rashi (according to Divrei David 1 ): 'Do not promise to testify for someone who claims falsely (even if in the end, you do not testify)'.
Seforno: It is a prohibition against combining with a Rasha to sign on a document.
Yevamos 25a: It is a prohibition against testifying together with a Rasha.
Sanhedrin 27a: It is a prohibition against the Dayanim accepting testimony of a Rasha.
Mechilta #1: It is a prohibition against Reuven saying to Shimon 'Levi owes me two hundred Dinrim; and I have one witness. Come and combine with him and you and I will take one Manah each'.
Mechilta #2: Based on this Pasuk the refined people of Yerushalayim would not participate in a Seudah until they knew who would join them there and would not sign on a Get until they knew who would co-sign with them. 2
Ibn Ezra: It is a prohibition agains a witness asking someone else to testify falsely together with him.
R. Chaim Paltiel: It is a prohibition against the Dayanim accepting false testimony, and placing the blame on the head of the witnesses.
Bava Kama, 72b: It disquaifies the testimony of an Eid Zomem retroactively (from the time that he testifies) - because from the time that he testifies he is a Rasha, and the Torah writes "Al Tashes Yadcha im Rasha" ('Al Tashes Rasha Eid'.
Sanhedrin, 27a #1: It is a prohibition against a Mumar (an apostate) who eats Neveilos, whether it is for pleasure or out of spite - testifying, since he is a Rasha, and the Torah writes "Al Tashes Yadcha im Rasha" ('Al Tashes Rasha Eid'). 3
Sanhedrin, 27a #2: "Al Tasheis Yadcha ... " ('Al Tashes Chamas Eid'): It is a prohibiton against robbers, people who lend on interest and people who renegue on their Shevu'os testifying. 4
What is "Lih'yos Eid Chamas" coming to add?
Seforno: In the event that you testify together with a Rasha, it transpires that you are a single [Kosher] witness, and Beis-Din will pervert justice by exacting money from the litigant against whom you are testifying on the basis of your testimony alone.
Mechilta: An example of an Eid Chamas is someone who is asked by his Rebbe to join a second witness to extract a Manah from his debtor - even though one know that, for all the money in the world, his Rebbe would not lie.
Why is this Pasuk written after the Pasuk of T'reifah?
Hadar Zekenim: Because one who testifies falsely deserves to be thrown to the dogs. 1
Like Izevel, who commanded witnesses to testify falsely about Navos (Melachim 1 21:8-10), and who was subsequently eaten by dogs (Melachim 2, 9:36). Refer also to 23:1:1:6*.
