Reference for Rosh Hashanah 4:3
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:
In the beginning, the lulav was taken in the mikdash seven days, [it being written (Leviticus 23:40): "And you shall rejoice before the L-rd your G-d seven days"], and in the medinah, one day, [viz. (Ibid.): "And you shall take for yourselves on the first day."] When the Temple was destroyed, R. Yochanan b. Zakkai instituted that the lulav be taken in the medinah seven days in remembrance of the mikdash and that the day of "hanef" [the waving of the omer (i.e., the sixteenth of Nissan)] be entirely forbidden [in the eating of "chadash" (see Succah 3:12)].