Reference for Niddah 53:40

יתיב רב פפא אחורי דרב ביבי קמיה דרב המנונא ויתיב וקאמר

lay thy hand upon thy mouth.<span class="x" onmousemove="('comment',' Prov. XXX, 32; he will not be able to give an authoritative answer when a question on the subject is addressed to him. ');">³⁶</span>

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