THE GREAT WONDER
The Mechaber in Shulchan Aruch (O. Ch. 580) lists additional fast days.
One of the fast days is on the 9th day in Teves. “It is unknown what
Tzoroh happened on that day”.
The Taz writes" תימה גדולה (It's a great wonder) that the Bais Yosef
doesn't know what happened that day. In our Selichos (Ezkero Motzok)
it is written that Ezra Hasofer died on the 9th of the month".
It is interesting, this Piyut is said, only by Ashkenazim. The Sefardim
say the Piyut “Sha’a Elyon” and the Piyut “Yoshev Bashomayim”.
In both of these Piyutim, it is mentioned that Ezra Hasofer died on the
10th of Teves.
The Mechaber, being Sefardi, must have held that Ezra died
on the 10th and therefore there shouldn't be a wonder why he
didn’t know what happened on the 9th of Teves.
The Tosfos Chadoshim on Megillas Ta’anis writes that
Yeisho Hanotzri ym”s was born on the 9th of Teves.
Chazal were scared of the Nochrim, to publicize
that we fast on his birthday.