Reference for Niddah 29:57

וסתות דרבנן

for he is of the opinion that [the laws relating to] settled period are only Rabbinical.<span class="x" onmousemove="('comment',' Sc. the Rabbis required a woman to examine herself when the date of her settled period arrives in order to ascertain whether there was a discharge or not. If, however, her husband was out of town and on his return it was unknown to him whether she did or did not examine herself she is not to be regarded as being in a condition of doubtful uncleanness. ');">⁵⁰</span>

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