My understanding was that Al HaNissim was established by the Geonim. Therefore, if you forget it during Shmone Esrei or during Birchas HaMazon one does not need to recite them again. From the discussion in today's Daf it appears that Al HaNissim was around in the time of the Gemara. So when was it established, and to clarify, what is the Halacha if it is forgotten?
Yours truly,
Asher Breatross
Shalom
I was unable to locate the source of Al haNisim. The Halacha is clear (OC 682:1) that if a person forgot Al haNisim and he already concluded the brocha, he does not return to say Al haNisim (in Sh'monah Esrei or Bircas haMazon). He should however, say it before "Yih'yu l'ratzon" (or Harachaman in the case of Bircas haMazon), in a form of request (MB ibid:4)
Yehuda Landy
Note that the reason that one does not need to repeat Birchas HaMazon if one forgot Al HaNissim during _Birchas haMazon_ is because one is not obligated to have a bread meal; similarly Yaaleh V'yovo on Rosh Chodesh or Chol HaMoed.
The rules for Shmone Esrei are different.
Kol Tuv
Meir Eliezer Bergman
Manchester UK