Reference for Rosh Hashanah 39:6

מדכולהו לאו משום דמצוה לקדש על הראייה ניסן ותשרי נמי לאו משום דמצוה לקדש על הראייה

Now if you say that the Adar preceding Nisan is sometimes full and sometimes defective, there is no difficulty: for the reason mentioned we allow the profanation of the Sabbath. But if you say that it is always defective, why should we allow the profanation?<span class="x" onmousemove="('comment',' Seeing that the observation makes no difference.');">⁷</span>

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