Question: If one prays Shacharit on a regular weekday under the mistaken assumption that it is Rosh Chodesh and inserts “Ya’aleh Ve’Yavo” into the Amida prayer, must one repeat the Amida prayer?
Answer: This question would apply to any addition in the prayer that is not applicable on that given day. For instance, if one inserts “Ata Chonantanu” into a regular weeknight Arvit or “Retzeh Vehachalitzenu” into a weekday Birkat Hamazon.
Does such an insertion constitute an interruption in the middle of one’s prayer and Birkat Hamazon such that if one becomes aware only after one concluded the prayer or Birkat Hamazon, one must repeat it, or is such an insertion not considered an interruption?
The Opinion of the Orchot Chaim
Maran Ha’Bet Yosef (Chapter 108) quotes the Orchot Chaim regarding one who forgot to pray Mincha on Shabbat in which case this individual must pray Arvit on Motza’ei Shabbat twice with the second acting as a compensatory prayer. In this case, the first Amida prayer corresponding to Arvit must include “Ata Chonantanu” as usual on Motza’ei Shabbat and the second prayer which serves to compensate for Mincha will not include “Ata Chonantanu.” Nevertheless, if one inserted “Ata Chonantanu” into the second Amida prayer as well, this is not considered an interruption of speech in the middle of one’s prayer and one need not repeat the Amida. The Bet Yosef derives from here that any mistaken addition to the Amida which is not applicable to that specific day is not considered an interruption and one has fulfilled one’s obligation.
The Shulchan Aruch
Thus, the Shulchan Aruch rules (ibid.) that if one mentions “Ya’aleh Ve’Yavo” and the like in one’s prayer on a day when it is not applicable, this is not considered an interruption and one need not repeat one’s prayer.
The Dispute in Understanding Maran
Some say that Maran only means this is not an interruption in a compensatory prayer, such as reciting “Ata Chonantanu” in both prayers on Motza’ei Shabbat. On the other hand, others disagree and explain Maran as meaning that it is never considered an interruption regardless of what prayer it is.
The Bottom Line
It seems that according to the letter of the law, any time one inserts a text for a special time, such as “Ya’aleh Ve’Yavo” or “Ata Chonantanu,” this is not considered an interruption of one’s prayer. Nevertheless, out of reverence for the Poskim who write that it is, one should preferably pray again while stipulating that if he is obligated to pray, it should be considered an obligatory prayer and if not, it should be considered a voluntary prayer. It seems that regarding Birkat Hamazon, one should not repeat it at all.
(Sources: See Yabia Omer, Volume 9, Chapter 94, Section 19; Halichot Olam, Volume 1, page 180; Yalkut Yosef, page 612. Based on the Poskim who derive this law from “Ata Chonantanu” and from the Mishnah Berura who rules that according to all Poskim it is not considered an interruption regarding “Ata Chonantanu” and nevertheless, Maran equated the law of any mistakenly inserted text to it, it seems that there should be no difference between them, in accordance with the ruling of the Yalkut Yosef.)