The Talmud discusses the source text for rabbinic commandments — 'lo tasur' (Deut. 17:11) — and asks whether blessings should be recited over mide-rabbanan mitzvot, debating the nature and force of rabbinic legislation.
מַאי מְבָרֵךְ? — מְבָרֵךְ: ״אֲשֶׁר קִדְּשָׁנוּ בְּמִצְוֹתָיו וְצִוָּנוּ לְהַדְלִיק נֵר שֶׁל חֲנוּכָּה״. וְהֵיכָן צִוָּנוּ? רַב אַוְיָא אָמַר: מִ״לֹּא תָסוּר״. רַב נְחֶמְיָה אָמַר: ״שְׁאַל אָבִיךָ וְיַגֵּדְךָ זְקֵנֶיךָ וְיֹאמְרוּ לָךְ״. מֵתִיב רַב עַמְרָם: הַדְּמַאי, מְעָרְבִין בּוֹ וּמִשְׁתַּתְּפִין בּוֹ וּמְבָרְכִין עָלָיו וּמְזַמְּנִין עָלָיו וּמַפְרִישִׁין אוֹתוֹ עָרוֹם וּבֵין הַשְּׁמָשׁוֹת. וְאִי אָמְרַתְּ כׇּל מִדְּרַבָּנַן בָּעֵי בְּרָכָה, הָכָא כִּי קָאֵי עָרוֹם הֵיכִי מְבָרֵךְ? וְהָא בָּעֵינַן וְהָיָה מַחֲנֶיךָ קָדוֹשׁ — וְלֵיכָּא! אָמַר אַבָּיֵי: וַדַּאי דְּדִבְרֵיהֶם בָּעֵי בְּרָכָה, סָפֵק דְּדִבְרֵיהֶם לָא בָּעֵי בְּרָכָה.
And what blessing does one recite? He recites: Who has made us holy through His commandments and has commanded us to light the Hanukkah light. The Gemara asks: And where did He command us? The mitzva of Hanukkah is not mentioned in the Torah, so how is it possible to say that it was commanded to us by God? The Gemara answers that Rav Avya said: The obligation to recite this blessing is derived from the verse: “You shall not turn aside from the sentence which they shall declare unto you, to the right, nor to the left” (Deuteronomy 17:11). From this verse, the mitzva incumbent upon all of Israel to heed the statements and decrees of the Sages is derived. Therefore, one who fulfills their directives fulfills a divine commandment. Rav Neḥemya said that the mitzva to heed the voice of the Elders of Israel is derived from the verse: “Ask your father, and he will declare unto you, your Elders, and they will tell you” (Deuteronomy 32:7). Rav Amram raised an objection from that which we learned in a mishna: With regard to doubtfully tithed produce [demai], i.e., grain that was acquired from an am ha’aretz about which there is uncertainty whether or not he tithed it; one may use it to establish an eiruv, i.e., joining of courtyards and joining of borders, and to establish the merging of alleys, and one recites a blessing before and after eating it, and one invites a quorum for recitation of Grace after Meals after eating it. Although the Sages said that one is required to separate tithes from demai, they allowed it to be used for specific purposes and in exigent circumstances. And they said that one may separate the tithe from demai when he is naked and at dusk Shabbat eve, a time when separating tithes from actual untithed produce [tevel] is prohibited. And if you say that every action instituted by rabbinic ordinance requires a blessing, as fulfillment of rabbinic ordinances is based on the mitzva: You shall not turn aside, here, when he stands naked, how can he recite a blessing? Don’t we require fulfillment of the mitzva: “Therefore shall your camp be holy; that He see no unseemly thing in you, and turn away from you” (Deuteronomy 23:15)? And the camp is not holy when one recites a blessing in a state of nakedness. Abaye said: There is room to distinguish between the cases: In a case where there is a definite mitzva by rabbinic law, a blessing is required. In a case where there is a rabbinic ordinance instituted due to uncertainty with regard to the circumstances, as in the case of demai, which may or may not have been tithed already, a blessing is not required.