2,079. Neglecting to Check

Hilchos Issurei Biah 6:20

Let’s say that a niddah checks herself during her niddah days and sees that her bleeding has stopped – even if it’s the second day of her period – and then, either intentionally or unintentionally, she doesn’t check herself again until many days after her niddah days and she finds impurity. In such a case, we don’t say that she was unclean the entire time and therefore a zavah. Rather, we operate under the assumption that she was ritually clean the entire time that she didn’t check. If she checked and found impurity, even on the seventh of her niddah days, then if she doesn’t check again before twilight in order to purify herself, but rather she waited days to check herself and found that she was clean, then there is a doubt as to whether she’s a zavah. If she found impurity, she is certainly a zavah; since she found impurity at both the beginning and the end, we operate under the assumption that she never stopped bleeding. On the first day of niddah, even if a woman found that she was clean, it’s treated as if she found impurity. This is because on the first day of niddah we operate under the assumption that a woman’s period will continue.

Hilchos Issurei Biah 6:21

If a zavah checks herself on the first counting day and finds herself ritually clean and then doesn’t check again until the seventh day, again finding herself clean, she is assumed to be ritually clean. It’s considered as if she checked herself on each of the seven days and found herself to be clean.