The Shulchan Aruch · Orach Chayim
אורח חיים ק״כOrach Chayim 120
Siman 120 of 697 in Orach Chayim — 1 se'if
הלכות תפילהLaws of Prayer· siman 120
Se’if 1א׳
אוֹמְרִים רְצֵה בְּכָל הַתְּפִלּוֹת, וּדְלֹא כְּאוֹתָם שֶׁנּוֹהֲגִים שֶׁלֹּא לְאָמְרוֹ בְּמִנְחָה.
That It Is Proper To Say "R'tzei" in Every [Amidah] Prayer. Containing 1 S'if: We say "R'tzei" in all the [Amidah] prayers; and this is not like those who have a custom to not say it in the afternoon [Amidah] prayer.
Shulchan Aruch, Orach Chayim — Torat Emet 363 edition, via Sefaria — public domain
English: Sefaria Community Translation — CC0