כֵּיצַד מְאַיְּמִין אֶת הָעֵדִים עַל עֵדֵי נְפָשׁוֹת, הָיוּ מַכְנִיסִין אוֹתָן וּמְאַיְּמִין עֲלֵיהֶן. שֶׁמָּא תֹאמְרוּ מֵאֹמֶד, וּמִשְּׁמוּעָה, עֵד מִפִּי עֵד וּמִפִּי אָדָם נֶאֱמָן שָׁמַעְנוּ, אוֹ שֶׁמָּא אִי אַתֶּם יוֹדְעִין שֶׁסּוֹפֵנוּ לִבְדֹּק אֶתְכֶם בִּדְרִישָׁה וּבַחֲקִירָה. הֱווּ יוֹדְעִין שֶׁלֹּא כְדִינֵי מָמוֹנוֹת דִּינֵי נְפָשׁוֹת. דִּינֵי מָמוֹנוֹת, אָדָם נוֹתֵן מָמוֹן וּמִתְכַּפֵּר לוֹ. דִּינֵי נְפָשׁוֹת, דָּמוֹ וְדַם זַרְעִיּוֹתָיו תְּלוּיִין בּוֹ עַד סוֹף הָעוֹלָם, שֶׁכֵּן מָצִינוּ בְקַיִן שֶׁהָרַג אֶת אָחִיו, שֶׁנֶּאֱמַר (בראשית ד) דְּמֵי אָחִיךָ צֹעֲקִים, אֵינוֹ אוֹמֵר דַּם אָחִיךָ אֶלָּא דְּמֵי אָחִיךָ, דָּמוֹ וְדַם זַרְעִיּוֹתָיו. דָּבָר אַחֵר, דְּמֵי אָחִיךָ, שֶׁהָיָה דָמוֹ מֻשְׁלָךְ עַל הָעֵצִים וְעַל הָאֲבָנִים. לְפִיכָךְ נִבְרָא אָדָם יְחִידִי, לְלַמֶּדְךָ, שֶׁכָּל הַמְאַבֵּד נֶפֶשׁ אַחַת מִיִּשְׂרָאֵל, מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ אִבֵּד עוֹלָם מָלֵא. וְכָל הַמְקַיֵּם נֶפֶשׁ אַחַת מִיִּשְׂרָאֵל, מַעֲלֶה עָלָיו הַכָּתוּב כְּאִלּוּ קִיֵּם עוֹלָם מָלֵא. וּמִפְּנֵי שְׁלוֹם הַבְּרִיּוֹת, שֶׁלֹּא יֹאמַר אָדָם לַחֲבֵרוֹ אַבָּא גָדוֹל מֵאָבִיךָ. וְשֶׁלֹּא יְהוּ מִינִין אוֹמְרִים, הַרְבֵּה רָשֻׁיּוֹת בַּשָּׁמָיִם. וּלְהַגִּיד גְּדֻלָּתוֹ שֶׁל הַקָּדוֹשׁ בָּרוּךְ הוּא, שֶׁאָדָם טוֹבֵעַ כַּמָּה מַטְבְּעוֹת בְּחוֹתָם אֶחָד וְכֻלָּן דּוֹמִין זֶה לָזֶה, וּמֶלֶךְ מַלְכֵי הַמְּלָכִים הַקָּדוֹשׁ בָּרוּךְ הוּא טָבַע כָּל אָדָם בְּחוֹתָמוֹ שֶׁל אָדָם הָרִאשׁוֹן וְאֵין אֶחָד מֵהֶן דּוֹמֶה לַחֲבֵרוֹ. לְפִיכָךְ כָּל אֶחָד וְאֶחָד חַיָּב לוֹמַר, בִּשְׁבִילִי נִבְרָא הָעוֹלָם. וְשֶׁמָּא תֹאמְרוּ מַה לָּנוּ וְלַצָּרָה הַזֹּאת, וַהֲלֹא כְבָר נֶאֱמַר (ויקרא ה) וְהוּא עֵד אוֹ רָאָה אוֹ יָדָע אִם לוֹא יַגִּיד וְגוֹ'. וְשֶׁמָּא תֹאמְרוּ מַה לָּנוּ לָחוּב בְּדָמוֹ שֶׁל זֶה, וַהֲלֹא כְבָר נֶאֱמַר (משלי יא) וּבַאֲבֹד רְשָׁעִים רִנָּה:
How did they admonish witnesses in capital cases? They brought them in and admonished them, [saying], “Perhaps you will say something that is only a supposition or hearsay or secondhand, or even from a trustworthy man. Or perhaps you do not know that we shall check you with examination and inquiry? Know, moreover, that capital cases are not like non-capital cases: in non-capital cases a man may pay money and so make atonement, but in capital cases the witness is answerable for the blood of him [that is wrongfully condemned] and the blood of his descendants [that should have been born to him] to the end of the world.” For so have we found it with Cain that murdered his brother, for it says, “The bloods of your brother cry out” (Gen. 4:10). It doesn’t say, “The blood of your brother”, but rather “The bloods of your brother” meaning his blood and the blood of his descendants. Another saying is, “The bloods of your brother” that his blood was cast over trees and stones. Therefore but a single person was created in the world, to teach that if any man has caused a single life to perish from Israel, he is deemed by Scripture as if he had caused a whole world to perish; and anyone who saves a single soul from Israel, he is deemed by Scripture as if he had saved a whole world. Again [but a single person was created] for the sake of peace among humankind, that one should not say to another, “My father was greater than your father”. Again, [but a single person was created] against the heretics so they should not say, “There are many ruling powers in heaven”. Again [but a single person was created] to proclaim the greatness of the Holy Blessed One; for humans stamp many coins with one seal and they are all like one another; but the King of kings, the Holy Blessed One, has stamped every human with the seal of the first man, yet not one of them are like another. Therefore everyone must say, “For my sake was the world created.” And if perhaps you [witnesses] would say, “Why should we be involved with this trouble”, was it not said, “He, being a witness, whether he has seen or known, [if he does not speak it, then he shall bear his iniquity] (Lev. 5:1). And if perhaps you [witnesses] would say, “Why should we be guilty of the blood of this man?,” was it not said, “When the wicked perish there is rejoicing” (Proverbs 11:10).]