Sukkah 41B

״עד עצם היום הזה״⁠ — עד עיצומו של יום, וקסבר ״עד״ ועד בכלל.

“And you should eat neither bread, nor roasted grain, nor fresh grain, until this selfsame [etzem] day, until you have brought the offering of your God” (Leviticus 23:14), indicating until the essence [itzumo] of the day, and not the night before. And he holds that when the verse states: “Until,” the word until is inclusive, meaning that the grain is permitted only after the conclusion of the 16th.

ומי סבר ליה כוותיה? והא מפליג פליג עליה, (דתניא:) משחרב בית המקדש, התקין רבן יוחנן בן זכאי שיהא יום הנף כולו אסור, אמר לו רבי יהודה: והלא מן התורה הוא אסור, דכתיב: ״עד עצם היום הזה״⁠ — עד עיצומו של יום!

The Talmud asks: And does Rabban Yoḥanan ben Zakkai hold in accordance with the opinion of R' Yehuda? But doesn’t he disagree with him, as it is taught in a baraita: Once the Temple was destroyed, Rabban Yoḥanan ben Zakkai instituted that for the entire day of waving the omer offering, it should be prohibited to eat the grain of the new crop. R' Yehuda said to him: Isn’t it prohibited by Torah law, as it is written: “Until this selfsame day,” which means: Until the essence of the day? Apparently, they have two divergent opinions.

רבי יהודה הוא דקא טעי, הוא סבר מדרבנן קאמר. ולא היא, מדאורייתא קאמר. והא ״התקין״ קאמר! מאי ״התקין״⁠ — דרש והתקין.

The Talmud answers: It is R' Yehuda who is mistaken. He thought that Rabban Yoḥanan ben Zakkai is saying it is prohibited by rabbinic law. And that is not so; he is saying it is prohibited by Torah law. The Talmud asks: But didn’t the Mishnah say: Rabban Yoḥanan ben Zakkai instituted, indicating that it is a rabbinic ordinance? The Talmud answers: What is the meaning of instituted? It means that he interpreted the verses in the Torah and instituted public notice for the multitudes to conduct themselves accordingly.