Nehemiah 8:14

And they found written in the law which the Lord had commanded
by Moses
The children of Israel, to be observed by them; either by hearing it read the day before, or by conversation with Ezra, they perceived it was enjoined in the law, particularly in ( Leviticus 23:39-43 ) ( Deuteronomy 16:13 )

that the children of Israel should dwell in booths, in the feast of the
seventh month:
which was the same month, and this the second day of it, and therefore the time drew near for keeping it; for it was to begin the fifteenth.