Niddah 65 - The First Night
When a virgin marries, it is to be expected that the rupturing of her hymen will cause her to bleed. This blood, of course, is not menstrual blood, and it does not render her either ritually impure or prohibited to her husband. Moreover, since the wound may take some time to heal, quite often a newlywed virgin may continue to experience bleeding for some time. How long can the blood be attributed to this, and after what time must one suspect that this is blood of a menstrual cycle, is discussed in the following rulings.
If a young girl whose time to discharge blood has not yet arrives (before twelve) gets married, then Beit Shammai give her the four nights during which all blood is deemed to be hymen blood, but Beit Hillel extend this until the wound heals. If her time to discharge blood arrived, but she has not seen blood yet (between twelve and twelve-and-a-half), and she got married, then Beit Shammai give her the first night, but Beit Hillel give her four nights, until Shabbat (as marriages usually happened on Wednesday). Finally, if she already experienced menstrual cycles before she got married, then Beit Shammai give her only the first cohabitation - which is a mitzvah - but Beil Hillel give her the entire first night.
Art: Jean-Baptiste-Camille Corot - Jewish Algerian Woman