Q. My grandfather told me that in his shul in the ‘alter haim’ (old country), when Rosh Hashana fell on Shabbos, they did not kneel on aleinu leshabeach. I have told to many including Rabbonim, about this minhag and they all tell me that it is incorrect and all do kneel on Shabbos. Is that true?
A. Indeed, Eishel Avrohom (Butchatch 621), Hago’os Chochmas Shlomo (592), Piskei Teshuvos (591: 3: n. 12) mention that some have a minhag not to kneel on Rosh Hashono and some even on Yom Kippur when it coincides with Shabbos. Some maintain that on those days only the Shaliach Tzibur prostrates. (They mention as a reason, that on Shabbos we are more careful not to get dust on our clothing and then unwittingly removing it, or because one may fix gaps on the ground).
Rabbi A. Bartfeld as advised by Horav Shlomo and Horav Aharon Miller Shlit’a