Reference for Shevuot 35:9

אמר ליה אי תניתא חסר ותני הכי זו היא מצות לא תעשה שבנדה שחייבין עליה היה משמש עם הטהורה ואמרה לו נטמאתי ופירש מיד חייב זו היא מצות עשה שבנדה כו'

Said Raba to him [R'Adda]; Listen to what your teacher [Rabina]<span class="x" onmousemove="('comment',' [So curr. ed. Other reading adopted by Adreth and Zerahis Halevi: 'He (Rabina) said to him (R. Adda) : Listen when your teacher (Raba) tells you.' This is preferable, as Raba was the teacher of Rabina.]');">²⁰</span> tells you.<span class="x" onmousemove="('comment',' That the Mishnah cannot refer to withdrawing. ,hmt');">²¹</span> - [He replied:] How can you [maintain that it refers to entering],<span class="x" onmousemove="('comment',' [Read with MS. M. and other ed.: , 'How can I listen?']');">²²</span>

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