אֶחָד בֵּית דִּין הַגָּדוֹל וְאֶחָד סַנְהֶדְרִין קְטַנָּה אוֹ בֵּית דִּין שֶׁל שְׁלֹשָׁה צָרִיךְ שֶׁיִּהְיֶה אֶחָד מֵהֶן סָמוּךְ מִפִּי הַסָּמוּךְ. וּמשֶׁה רַבֵּנוּ סָמַךְ יְהוֹשֻׁעַ בַּיָּד שֶׁנֶּאֱמַר (במדבר כז כג) "וַיִּסְמֹךְ אֶת יָדָיו עָלָיו וַיְצַוֵּהוּ". וְכֵן הַשִּׁבְעִים זְקֵנִים משֶׁה רַבֵּנוּ סְמָכָם וְשָׁרְתָה עֲלֵיהֶן שְׁכִינָה. וְאוֹתָן הַזְּקֵנִים סָמְכוּ לַאֲחֵרִים וַאֲחֵרִים לַאֲחֵרִים וְנִמְצְאוּ הַסְּמוּכִין אִישׁ מִפִּי אִישׁ עַד בֵּית דִּינוֹ שֶׁל יְהוֹשֻׁעַ וְעַד בֵּית דִּינוֹ שֶׁל משֶׁה רַבֵּנוּ. וְאֶחָד הַנִּסְמָךְ מִפִּי הַנָּשִׂיא אוֹ מִפִּי אֶחָד מִן הַסְּמוּכִין אֲפִלּוּ לֹא הָיָה אוֹתוֹ סָמוּךְ בַּסַּנְהֶדְרִין מֵעוֹלָם:
At least one of the members of the Supreme Sanhedrin, a minor Sanhedrin, or a court of three must have received semichah (ordination) from a teacher who himself had been given semichah. Our teacher, Moses ordained Joshua by placing his hands upon him, as Numbers 27:23 states: "And he placed his hands upon him and commanded him." Similarly, Moses ordained the 70 judges and the Divine presence rested upon them. Those elders ordained others, and the others still others in later generations. This tradition continued until the Talmudic era, when the Sages had received ordination one from the other in a chain extending back to the court of Joshua, and to the court of Moses. A person who is ordained by the nasi and one ordained by another ordained judge have the same status, even if that ordained judge never served in a Sanhedrin.
