Reference for Rosh Hashanah 40:8

למאי נפקא מינה אמר רב אשי לאכחושי סהדי

When R'Zera went up [to Palestine], he sent back word to them [in Babylon]: It is necessary that there should be [on New Moon] a night and a day of the new moon.<span class="x" onmousemove="('comment',' I.e., that there should be no appearance of the old moon in this period, viz., after the closing of the twenty-ninth day; otherwise New Moon cannot be proclaimed on the thirtieth.');">⁵</span>

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