A grammatical question about Shabbes davening

Question

I recently noticed that in my siddur (Siddur Vilna), in the fourth berakha of the Shabbes davening (או"א רצה במנוחתינו...), there's a pronominal suffix near the conclusion that changes depending on whether it is Maariv, Shacharis/Mussaf or Mincha.

On Maariv, one says וינוחו בה (the feminine singular ending), on Shacharis/Mussaf one says וינוחו בו (the masculine singular ending), and on Mincha one says וינוחו בם (the masculine plural ending).

I have checked, and have found this difference also in my Chabad siddur, Torah Or, as well as other siddurim that (like Siddur Vilna) also testifying to the minhagim of the Gra. Siddur Vilna sources it in a sefer called Olas Shabbes, and notes that this custom (while it is not universal) is also mentioned in the Eliyahu Zuta on the Levush, and by the Magen Avraham.

My question is a grammatical one.

If we use the feminine singular ending (such as some do on Maariv), the referent is Shabbes - understood as a feminine word.

If we use the masculine singular ending (such as some do on Shacharis/Mussaf), the referent is Shabbes - understood as a masculine word (see here and here).

If we use the masculine plural ending... what is the referent? Shabbes and something else?

Answer 1

@DoubleAA alluded to Aruch Hashulchan. Indeed, p. 3 of this article cites Aruch Hashulchan 268:14 explaining the reasons of the feminine and masculine aspects of Shabbat. In Mincha, the uses of בם is a reference to both of these aspects. I haven't yet read the full original source to understand why both ideas need to be included and why this is done during Mincha.

Keep in mind, though, that the whole concept of making any change whatsoever is a much later concept from the original version from Rav Sa'adiah and Rav Amram's siddurim. Read the rest of the linked article to understand the history.

Answer 2

The סדר עבודת ישראל by Baer (see here for Wikipedia article on him) writes on page 263 that the usage of saying בָהּ, בוֹ, בם on Friday night, Shabbos day and Shabbos mincha as referred to by the authorities you quote, is something amazing and against all usage of the language. Therefore he uses בָהּ all three times.

So Baer holds that there is no referent for either of the masculine endings.

Possible מעשה לסתור - story against my answer: A friend acting as chazzan on Shabbos afternoon said שבתות קדשך which as Double AA says fits better with בם . A respected Rav present in the minyan asked him why he had made the change and on hearing the answer said that he should have stayed with the accepted nusach of שבת קדשך, וינוחו בם.