Mishnayos Makkos Perek 1 Mishnah 8

The mishna cites another derivation based on the juxtaposition of two to three: And just as with regard to two witnesses, if one of them is found to be a relative or is otherwise disqualified, their entire testimony is voided, as it is no longer the testimony of two witnesses, so too, with regard to three witnesses who came to testify as one set, if one of them is found to be a relative or is otherwise disqualified, their entire testimony is voided, even though two valid witnesses remain. From where is it derived that the same halakha applies even in the case of one hundred witnesses? It is derived from a verse, as the verse states: “Witnesses.” Rabbi Yosei says: In what case is this statement, that if one of the three witnesses is disqualified the entire testimony is voided, said? It is said with regard to cases of capital law, which are adjudicated stringently. But with regard to cases of monetary law, which are adjudicated more leniently, even if one of the witnesses is disqualified, the testimony will be validated with the testimony of the rest of the witnesses, and if it is sufficient the case can be adjudicated on that basis. Rabbi Yehuda HaNasi disagrees and says: If one of the three witnesses is disqualified the entire testimony is voided in both cases of monetary law and cases of capital law. And when does one disqualified witness void the entire testimony? Only when the witnesses forewarned them before they performed the transgression, thereby demonstrating their desire to fill the role of witnesses in that case. But when they did not forewarn them, what shall two brothers do in a case where they, together with others, saw someone who killed a person? Will the murderer escape punishment because two relatives happened to be there at the time of the murder and their presence voids the entire testimony? No, the testimony is voided by the presence of relatives or disqualified witnesses only when their intent was to testify. If that was not their intent, they do not void the testimony.

מַה שְּׁנַיִם נִמְצָא אַחַד מֵהֶן קָרוֹב אוֹ פָסוּל עֵדוּתָן בְּטֵלָה, אַף שְׁלשָׁה נִמְצָא אֶחָד מֵהֶן קָרוֹב אוֹ פָסוּל, עֵדוּתָן בְּטֵלָה. מִנַּיִן אֲפִלּוּ מֵאָה, תַּלְמוּד לוֹמַר, עֵדִים. אָמַר רַבִּי יוֹסֵי, בַּמֶּה דְבָרִים אֲמוּרִים, בְּדִינֵי נְפָשׁוֹת. אֲבָל בְּדִינֵי מָמוֹנוֹת, תִּתְקַיֵּם הָעֵדוּת בַּשְּׁאָר. רַבִּי אוֹמֵר, אֶחָד דִּינֵי מָמוֹנוֹת וְאֶחָד דִּינֵי נְפָשׁוֹת. בִּזְמַן שֶׁהִתְרוּ בָהֶן, אֲבָל בִּזְמַן שֶׁלֹּא הִתְרוּ בָהֶן, מַה יַּעֲשׂוּ שְׁנֵי אַחִין שֶׁרָאוּ בְאֶחָד שֶׁהָרַג אֶת הַנָּפֶשׁ: