Reference for Niddah 72:50
אמר קרא תשב יש לך ישיבה אחרת שהיא כזו ואיזו זו זו קושי בימי זיבה
but hold that which is due to an accident unclean since it is not followed by cleanness. On the contrary! That which is due to an accident should be held clean since a discharge from a <i>zab</i> that is due to an accident is clean? — Now at all events we are dealing with the case of a woman, and we do not find that in the case of a woman blood due to an accident is ever clean. And if you prefer I might reply: What opinion do you hold? Is it to regard a discharge that is due to an accident clean and one that is due to childbirth unclean? Surely you cannot point to any occurrence that is more in the nature of an accident<span class="x" onmousemove="('comment',' Sc. that is not dependent on the woman's will. ');"><sup>40</sup></span>