2,109. Stains on Garments
Hilchos Issurei Biah 9:11
If the woman was in the habit of removing her garment and using it to cover herself at night, then she is rendered ritually unclean wherever a blood stain might be found on it. The same is true of her girdle: if blood is found anywhere on it, she is rendered ritually unclean.
Hilchos Issurei Biah 9:12
Let’s say that a woman wore the same tunic for three or more days not during her niddah days. She then inspected it and found three blood stains or one stain that's as large as three stains combined. In such a case, there’s a doubt as to whether or not she’s a zavah because it’s possible that she stained the garment on each of the three days. The same is true if she wore three garments simultaneously for three days during her zivah days. If she inspected these garments and found a stain in each of them, then there’s a doubt as to whether or not she’s a zavah. This is so even if the stains all line up in a row.