Halakhah zu Tehillim 119:142

After the repetition of the Shemoneh esreih we are accustomed to say "Tzidkasecha tzedek …" ["Your righteousness is righteousness everlasting"] which consists of three verses³⁹Psalms 119: 142, 71: 19, 36: 7. This is the order of Nusach Ashkenaz. The order of Nusach Sefard is the reverse. that are similar to "Tzidduk Hadin."⁴⁰Tzidduk Hadin is a special prayer which is said at the graveside expressing God’s righteousness and our acceptance of the Divine decree. [These verses express our acceptance of Divine decree] on the death of three Tzaddikim [pious souls] who passed away at this time [Shabbos afternoon]: Yoseph, Moshe and Dovid.⁴¹Zohar, Vol. 2, 156a. (Parshas Terumah). If Shabbos occurs on a day where if it were a weekday Tachanun would not be said,⁴²See chapter 22. Tzidkassecha tzedek is not said. But when praying with a congregation in the house of a mourner, it is said,⁴³Even though ordinarily Tachanun is not said in a mourner’s house. for if it would not be said it would be a public demonstration of mourning⁴⁴Seifer Tosafos Shabbos. However, Yosef Da’as, responsum 400, maintains as does Peri Megadim 131: 10, that even in private it is said in a mourner’s house. and public mourning is not permitted on Shabbos.