(Today’s Halacha was presented by HaGaon HaRav Shemuel Pinhasi Shelit"a of Jerusalem)
There is a discussion among the Halachic authorities concerning the case of a person who forgot to recite a required insert in the Amida prayer – such as Ya’aleh Ve’yabo or Mashib Ha’ru’ah – and realized his mistake immediately after reciting the words "Baruch Ata Hashem" at the end of that Beracha. Normally, if a person realizes after reciting "Baruch Ata Hashem" that the Beracha is recited in error, he is advised to immediately recite the words "Lamedeni Hukecha," so that he has recited a complete verse from Tanach ("Baruch Ata Hashem Lamedeni Hukecha" – Tehillim 119:12). This way, he avoids reciting a "Beracha Le’batala" (Beracha in vain). The question arises whether this applies even to a Beracha in the Amida. One might argue that reciting a verse from Tehillim would constitute a Hefsek (forbidden interruption) in the Amida, as it does not relate to the prayer service, in which case this solution may not employed in cases of mistakes during the Amida.
This issue is discussed by the Ritba (Rabbi Yom Tob Ben Abraham of Seville, Spain, 1250-1330), in his commentary to Masechet Megila, where he establishes a basic rule that has been accepted as Halacha. The Ritba writes that the Halacha in this case depends on whether or not the Beracha would indeed be recited in vain if it is completed. For example, if a person mistakenly recited "Barech Alenu" in the summer instead of "Barechenu," and he realizes his mistake after he recited the words "Baruch Ata Hashem" at the end of the Beracha, then if he completes the Beracha, it would have been recited in vain; he would have to recite "Barechenu" from the beginning. Therefore, upon realizing his mistake, he should recite "Lamedeni Hukecha" to avoid reciting a Beracha in vain. Although the verse "Baruch Ata Hashem Lamedeni Hukecha" is not part of the text of the Amida, it is nevertheless a prayer ("teach me Your statutes"), and it is therefore germane to the prayer service and does not constitute a Hefsek. The person should then recite "Barechenu" and proceed as usual.
This would also apply if one mistakenly recited "Mashib Ha’ru’ah" in the summer instead of "Morid Ha’tal," and he realized his mistake after he recited "Baruch Ata Hashem," before concluding "Mehayeh Ha’metim." Here, too, if he concludes the Beracha, it would be a "Beracha Le’batala" and he would have to return to the beginning of the Amida. Therefore, he should recite "Lamedeni Hukecha" and then return to recite "Morid Ha’tal."
However, there are situations where concluding the Beracha – even if it was recited with a mistake – would not render it a "Beracha Le’batala." For example, if one mistakenly omitted the "Ya’ale Ve’yabo" insert during Arbit on Rosh Hodesh, his Amida is nevertheless valid. Therefore, if during Arbit on Rosh Hodesh a person realized after reciting "Baruch Ata Hashem" – but before concluding "Ha’mahazir Shechinato Le’siyon" – that he forgot to add "Ya’ale Ve’yabo," he should simply conclude the Beracha and continue. Since the Beracha will not be regarded as a "Beracha Le’batala," it is preferable to simply recite the Beracha and proceed as usual, rather than reciting "Lamedeni Hukecha." However, if this occurredThis applies during on the day of Rosh Hodesh, as well, during at Shaharit or Minha. Although, when one who omits Ya’ale Ve’yabo at Shaharit or Minha on Rosh Hodesh does not fulfill his obligation, if he realizes his mistake immediately after reciting the Beracha of "Ha’mahazir Shechinato Le’siyon," he can recite Ya’ale Ve’yabo at that point, before "Modim." Although this issue is subject to a debate among the Rishonim, the Ritba rules that if one realizes his mistake after reciting "Baruch Ata Hashem," it is preferable to conclude with "Ha’mahazir Shechinato Le’siyon" and then he should recite "Lamedeni Hukecha"Ya’ale Ve’yabo at that point, rather than reciting "Lamedeni Hukacha." and then recite "Ya’ale Ve’yabo," rather then conclude the Beracha which would be a "Beracha Le’batala."
Summary: If a person forgot to recite a required insert in a Beracha in the Amida, and he realized his mistake immediately after reciting the words "Baruch Ata Hashem" at the end of that Beracha, and if he concludes the Beracha it would be regarded a "Beracha Le’batala," then he should recite the words "Lamedeni Hukecha" and then return to the insert he missed. However, if the Beracha would not be a "Beracha Le’batala," such as in the case of "Ya’ale Ve’yabo" at Arbit on Rosh Hodesh, then he should simply conclude the Beracha and proceed as usual. Therefore, if during Arbit on the night of Rosh Hodesh one forgot to recite Ya’ale Ve’yabo and he realized his mistake after reciting "Baruch Ata Hashem," he should simply conclude with "Ha’mahazir Shechinato Le’siyon" and proceed as usual. If this occurred during Shaharit or Minha of Rosh Hodesh, then he should conclude with "Ha’mahazir Shechinato Le’siyon" and then recite Ya’ale Ve’yabo at that point, before "Modim."
