Mishnayos Rosh Hashanah Perek 4 Mishnah 3

After the previous mishna mentioned Rabban Yoḥanan ben Zakkai’s ordinance that applies to the sounding of the shofar, this mishna records other ordinances instituted by the same Sage: At first, during the Temple era, the lulav was taken in the Temple all seven days of Sukkot, and in the rest of the country outside the Temple, it was taken only one day, on the first day of the Festival. After the Temple was destroyed, Rabban Yoḥanan ben Zakkai instituted that the lulav should be taken even in the rest of the country all seven days, in commemoration of the Temple. And for similar reasons, Rabban Yoḥanan ben Zakkai instituted that for the entire day of waving the omer offering, i.e., the sixteenth of Nisan, eating the grain of the new crop is prohibited. By Torah law, when the Temple is standing the new grain may not be eaten until after the omer offering is brought on the sixteenth of Nisan, usually early in the morning. When the Temple is not standing it may be eaten from the time that the eastern horizon is illuminated at daybreak. However, Rabban Yoḥanan ben Zakkai instituted a prohibition against eating the new grain throughout the entire sixteenth of Nisan, until the seventeenth, to commemorate the Temple.

בָּרִאשׁוֹנָה הָיָה הַלּוּלָב נִטָּל בַּמִּקְדָּשׁ שִׁבְעָה, וּבַמְּדִינָה יוֹם אֶחָד. מִשֶּׁחָרַב בֵּית הַמִּקְדָּשׁ, הִתְקִין רַבָּן יוֹחָנָן בֶּן זַכַּאי שֶׁיְהֵא לוּלָב נִטָּל בַּמְּדִינָה שִׁבְעָה זֵכֶר לַמִּקְדָּשׁ, וְשֶׁיְּהֵא יוֹם הָנֵף כֻּלּוֹ אָסוּר: