Nusach Ashkenaz says Psalm 27 during *ma'ariv* while Nusach Sefard says it during *mincha*. Let's say someone who usually davens Nusach Ashkenaz entered a Nusach Sefard shul for mincha. He accidentally said Psalm 27 during mincha. He goes to his Nusach Ashkenaz shul for Ma'ariv. Should he repeat saying Psalm 27? **Note:** - I am asking what he should do as a *yachid* (individual) and not a *shali'ach tzibbur*. In the latter case, I believe that the rule is that the Shat'z always follows the nusach of the shul.