Midrash for Zevachim 46:1
אם עון פיגול הרי כבר נאמר (ויקרא ז, יח) לא יחשב אם עון נותר הרי כבר נאמר (ויקרא ז, יח) לא ירצה
If the iniquity of piggul,<span class="x" onmousemove="('comment',' V. Glos.');"><sup>1</sup></span> surely it is already said, it shall not be accepted?<span class="x" onmousemove="('comment',' Lev. XIX, 7.');"><sup>2</sup></span>
Sifrei Devarim
(Devarim 18:5) "For in him (the Cohein) did the L-rd your G-d choose from all of your tribes to stand to serve in the name of the L-rd": We are hereby taught that his service is valid only standing, and if he sat and served, his service is invalid.
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