From Nehemiah, Chapter 8:
13 On the second day of the month, the heads of all the families, along with the priests and the Levites, gathered around Ezra the scribe to give attention to the words of the Law. 14 They found written in the Law, which the LORD had commanded through Moses, that the Israelites were to live in booths during the feast of the seventh month 15 and that they should proclaim this word and spread it throughout their towns and in Jerusalem: "Go out into the hill country and bring back branches from olive and wild olive trees, and from myrtles, palms and shade trees, to make booths"-as it is written.
16 So the people went out and brought back branches and built themselves booths on their own roofs, in their courtyards, in the courts of the house of God and in the square by the Water Gate and the one by the Gate of Ephraim. 17 The whole company that had returned from exile built booths and lived in them. From the days of Joshua son of Nun until that day, the Israelites had not celebrated it like this. And their joy was very great.
18 Day after day, from the first day to the last, Ezra read from the Book of the Law of God. They celebrated the feast for seven days, and on the eighth day, in accordance with the regulation, there was an assembly.
A few comments.
One, check out passage 15, specificially the supposedly quoted portion, i.e. "'Go out into the hill country and bring back branches from olive and wild olive trees, and from myrtles, palms and shade trees, to make booths' - as it is written."
Here it is in Hebrew:
צְאוּ הָהָר וְהָבִיאוּ עֲלֵי-זַיִת וַעֲלֵי-עֵץ שֶׁמֶן, וַעֲלֵי הֲדַס וַעֲלֵי תְמָרִים וַעֲלֵי עֵץ עָבֹת לַעֲשֹׂת סֻכֹּת, כַּכָּתוּב
Now, note how curiously they left out the whole 'pri etz hadar' section from Vayikra. The etrog has a pretty prominent place in modern observance of Succos, rather strange that they left it out, hmm? It seems to have been replaced here with olive branches. Could 'pri etz hadar' have meant olives in Nehemia's time? Think about it.
Also note how the Israelites are using those four species, not to shake about in a bundle, but to construct their Succot. The whole shaking ritual of the lulav and etrog is actually absent from the entire Tanach. It is not mentioned in Vayikra or here in Nehemiah or anywhere else in the Bible. Curious, no?
In fact, using the four species as building materials is the traditional understanding of the Biblical instructions as far as the Karaites are concerned. To this day, observant Karaites will build their Succah roofs with olive branches, along with myrtle, willow, and palm fronds. Typically they also reject the 'four wall' ideal of Rabbinic Judaism and build them tent-like as well.
Lastly, I'd like to point out passage 17, about how they had never celebrated like this and in passage 14 how they apparently discovered this festival in Ezra's Torah. For a group with a supposedly perfect transmission of data from the moment at Sinai, they seem to be awfully forgetful. What does this say to the Kuzari argument?
Just a few things to think over. And, of course, have a happy Succos.