Shulchan Arukh, Orach Chayim Siman 120
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.
שראוי לומר רצה בכל תפלה. ובו סעיף אחד
אומרים רצה בכל התפלות ודלא כאותם שנוהגים שלא לאומרו במנחה:
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.