Siman 598
Presented here for study, not as a practical ruling. The Shulchan Aruch rules by Sephardi custom, the Rema's glosses by Ashkenazi custom, and the Kitzur follows Ashkenazi custom. For a practical question, ask your rabbi.
א רֹאשׁ הַשָּׁנָה שֶׁחָל לִהְיוֹת בְּשַׁבָּת אוֹמְרִים צִדְקָתְךָ, בְּמִנְחָה. הַגָּה: וְיֵשׁ אוֹמְרִים שֶׁלֹּא לְאָמְרוֹ (רַ"ן סר"ה וּמִנְהָגִים), וְכֵן אָנוּ נוֹהֲגִים.
1 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.