The Sages taught [in a baraita with regard to Megillat Ta’anit, which is a list of days of redemption that were established as celebrations for generations:] Who wrote Megillat Ta’anit? [The scroll was written by] Hananya ben Hizkiya [ben Garon] and his faction.
The Koren notes:
Until the Mishna was written, writing the Oral Torah was prohibited. However, standard practice was to make certain lists exclusively for individual use e.g. the hidden scrolls.
Megillat Ta’anit was the first book, apart from the Bible, that was written. This scroll, which is available today, includes a list of days on which it is prohibited to eulogise the deceased or fast due to the miraculous and joyous events that transpired on those days.
The scroll is written in two languages: The primary halakha, the day and its legal status, is written in Aramaic, while the descriptions of what happened each day are in Hebrew.
The entire scroll was not written by Hananya ben Hizkiya and his son. Events were added in later generations, approximately until the redaction of the Mishna. A citation from Megillat Ta’anit with regard to Hanukah appears later in this tractate (21b).