Shulchan Arukh, Orach Chayim Siman 598
Can copy this into an AI, or connect the whole library to your assistant. For deeper learning, you can directly use the original seforim, sites, and apps.
ר"ה שחל להיו' בשב' אומרים צדקתך במנחה: הגה וי"א שלא לאומרו (ר"ן סר"ה ומנהגים וכן אנו נוהגים):
Mishna Berura Yomi
When Rosh HaShanah falls on Shabbat we say Tzidkatkhah at mincha. Rema: And there are those who say we do not say it [Ran end of Tractate Rosh HaShana and Minhagim], and this is our custom.