Shelosha Ve'esrim Umeya - mi yodeya?

Question

Who knows one hundred twenty-three?

Please cite/link your sources, if possible. At some point at least twenty-four hours from now, I will:

• Upvote all interesting answers.

• Accept the best answer.

• Go on to the next number.

Answer 1

When reciting Hallel responsively (the chazzan saying each stich of Hallel, and the congregation responding "Halleluyah"), they say "Halleluyah" 123 times. The Yerushalmi (Shabbos 16:1) associates this with the age of Aharon, and this is codified by Rambam (Hil. Chanukah 3:12).

In one of his talks (Likkutei Sichos, vol. 23, pp. 229ff), the Lubavitcher Rebbe zt"l explains the deeper reason behind this association: (a) this way of saying Hallel helps even those who aren't so literate be able to join in the recitation; (b) it means that everyone is reciting Hallel in unison. Both of these reflect Aharon's way of bringing everyone, regardless of their status, closer to Hashem ("אוהב את הבריות ומקרבן לתורה").

Answer 2

Aharon lived to 123.

Answer 3

Yitzchak, at 123, blessed Yaakov. (He was worried he'd die at an age within five years of the age of his mother's death, according to, um, someone.)

Answer 4

W.M. Feldman, in his book Rabbinical Mathematics and Astronomy (1931, reprinted 1978), suggests a cycle in which 123 out of every 334 years are leap years (instead of the 19-year cycle with 7 leap years that we use today), so that it keeps better pace with the solar year.

(This is of course of theoretical interest only, since we don't have a Sanhedrin that can make any such changes - and when we do, we'll go back to having Rosh Chodesh and leap years set on an observational basis, so that there won't be any fixed cycles.)

Answer 5

Asher the son of Yaakov Avinu lived for 123 years

Answer 6

Yishmael was 14 years older than Yitzchok. Yishmael died when he was 137, so Yitzchok was 123 years old when Yishmael died.