Reference for Arakhin 15:7

אין בערכין פחות מסלע ולא יתר כו':

<big><b>MISHNAH: </b></big>IF A WOMAN GOES ASTRAY<span class="x" onmousemove="('comment',' Lev. XV deals with the regulations touching the woman's issue (of blood) , and distinguishes between an issue 'in time of her impurity' and one 'not in' or 'beyond' the time of her impurity. The flow 'in the time of her impurity' is called dam niddah - the blood of her menstruation; the flow beyond or outside the time of her impurity is called dam zibah - the blood of one having an issue. According to the law of the Torah a woman who menstruates for the first time becomes unclean as niddah for seven days, the day on which she menstruated included. She remains in this state of uncleanness for seven days, independent of whether she has had that issue of blood for the first day only or on any other of the seven days. Even if she should suffer such issue for seven days continuously, as long as it has stopped before sunset on the seventh day, she takes the ritual bath that night and becomes clean thereby. These seven days are her niddah days. The eleven days following are called 'the days of her having an issue', yeme zibah, any issue of blood during which is considered 'not in' or 'beyond the time of her impurity'; this period starts at the end of the seven days of her normal impurity, quite independent of her having taken the bath prescribed or not. Any issue of blood on one of these eleven days renders the woman a zabah ketannah, one having a minor issue, and by taking the ritual bath on the day following the issue, she becomes clean if no new issue appeared on the day of the bath. The same law applies if on any other of the eleven days issue should have appeared. But if such issue appeared on three consecutive days, the woman's considered zabah gedolah, one having a major issue, and she does not regain her ritual cleanness until seven days. free from any issue following the last of the three days, have passed. On the seventh day she takes the ritual bath of purification, and on the eighth day she offers two turtle-doves as her sacrifice of purification. If during these eleven days there had been no issue of blood, or only a 'minor issue' then any day from the twelfth on, on which she should have an issue, is the commencement of her niddah days, yeme niddah. If, however, she had become during the eleven days zabah ge dolah, one having a major issue, then she does not become a niddah again until there have been seven days after the last day of the flow during which there was no issue whatsoever. Any issue of blood appearing before such seven days have passed is considered part of the days of zibah. Even after the days of her niddah have started she of course becomes a niddah only when and if she has an issue, yeme niddah signifying no more than that she becomes a niddah in case of any issue, as against her being a zibah during the other period. After she has become a niddah again she remains in this state for seven days. to be followed again by the days of zibah. A woman thus can become a zabah only in the eleven days following her yeme niddah; or, if during these eleven days she had three days' consecutive flow, she remains a zabah until she had had seven days of freedom from any flow. After that period she becomes a niddah again, with the first flow. And similarly a woman can become niddah again only after the passing of the eleven days of zibah, or, if during these days she had become a zabah gedolah, one having a large issue, she can become a niddah only after seven days have gone after the last day of the flow during which no further flow was experienced. Upon the day on which the woman becomes niddah again, depends the count of the rest of these days of her niddah state as well as the count of the days of her zibah. Therefore the day on which she becomes niddah is considered the 'entrance', the 'gate', the 're-opening'. The Mishnah refers to a woman 'astray in her reckoning', i.e., one who after purification has experienced a flow of blood, and does not remember whether she was passing through the days of niddah or those of her zibah. She is unable to emerge from this state of uncertainty to a new safe reckoning until after the end of the present flow she experiences a new one, as to which she is definitely sure that it was her period of niddah. This certainty cannot be obtained earlier than after seven days, nor later than after seventeen days, during which she experiences no flow of blood at all.');">³</span>

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