The special "Al Ha’nissim" paragraph for Purim is added to the Amida prayer at all three prayer services on Purim. One who mistakenly omitted this paragraph does not need to repeat the Amida.
This Halacha gives rise to an interesting question in the case of a person who recites the Amida at a slower pace than the congregation, and is still reciting the Amida when the Hazzan began the repetition. If the person thinks that he can complete the Amida in time to join the congregation in the recitation of "Nakdishach" if he skips "Al Ha’nissim," should he do so? Since omitting "Al Ha’nissim" does not disqualify one’s recitation of the Amida, perhaps it is preferable to skip "Al Ha’nissim" for the sake of being able to join in the recitation of "Nakdishach."
The rationale for such a conclusion would be the comment of the Ben Ish Hai (Rav Yosef Haim of Baghdad, 1833-1909), in Parashat Teruma (5), that the recitation of "Nakdishach," through which we publicly proclaim G-d’s sanctity, fulfills the Biblical Misva of "Ve’nikdashti Be’toch Beneh Yisrael" – "I shall be sanctified among Beneh Yisrael" (Vayikra 22:32). This is also the implication of the Zohar, in Parashat Emor. If reciting "Nakdishach" with the congregations fulfills a Biblical Misva, then one might assume that it is preferable to omit "Al Ha’nissim" – the recitation of which was, quite obviously, enacted by the Sages – in order to fulfill this Misva.
However, Hacham Ovadia Yosef, in Yabia Omer (2:32), rules otherwise. He demonstrates from numerous sources that the recitation of "Nakdishach" is a Misva enacted by the Sages, and does not actually fulfill a Torah obligation. Those sources which indicate that this recitation fulfills the Misva of "Ve’nikdashti" refer to this verse only as an "Asmachta" – an allusion in the Biblical text to a law enacted by the Sages. But in truth, the recitation of "Nakdishach" fulfills only a Rabbinic obligation. Therefore, since both "Nakdishach" and "Al Ha’nissim" are recited Mi’de’rabbanan (by force of Rabbinic enactment), it is preferable to recite the Amida properly, with "Al Ha’nissim," rather than omit it for the sake of reciting "Nakdishach." When the Hazzan reaches "Nakdishach," the individual should stop reciting the Amida and have in mind the words of "Nakdishach," as Halacha requires if one is in the middle of the Amida when the congregation recites "Nakdishach." This is also the ruling of Hacham Bension Abba Shaul (Israel, 1924-1998).
A fascinating insight into this topic was presented by Rav Natan Ben-Senior (contemporary). He notes that a careful reading of the relevant passage in the Zohar shows that according to the Zohar, the Misva of "Ve’nikdashti" is fulfilled in the mind. This verse requires sacrificing one’s life for Hashem if he is, Heaven forbid, put to the test, and we fulfill this Misva every time we make the commitment in our minds that we would be prepared to make such a sacrifice. When the Zohar says that reciting "Nakdishach" fulfills the Misva of "Ve’nikdashti," it means that the intention we have when we recite "Nakdishach," committing ourselves unconditionally to G-d, even if He calls upon us to make the ultimate sacrifice, Heaven forbid, fulfills this Misva. This point is perhaps alluded to in the formulation of the verse – "Ve’nikdashti Be’toch Beneh Yisrael," which could be understood to mean that G-d should be sanctified "in the midst" of each and every Jew, in every Jew’s mind and heart, as he commits to making the ultimate Kiddush Hashem should such a situation arise. Therefore, Rav Senior explained, even if one is unable to actually recite "Nakdishach," by thinking the words and committing himself to sanctify G-d’s Name even when put to the test, he fulfills the Biblical Misva of "Ve’nikdashti." And therefore, even if "Ve’nikdashti" indeed fulfills this Misva, one should not skip "Al Ha’nissim" in order to be able to recite "Nakdishach."
Summary: One who mistakenly omits "Al Ha’nissim" on Purim does not repeat the Amida. Nevertheless, one should not purposely skip "Al Ha’nissim" in order to complete the Amida in time to join the congregation in reciting "Nakdishach."
