Pesahim 80a and Pesahim 80b, how the ritual impurity of various segments of the Jewish people affects the ability to offer the Pesah sacrifice, when the 14th of Nisan Pesah will be done with ritual impurity, when it will be done in two groups, when there cannot be a Pesah Sheni, on the 14th of Iyyar. Then, which kinds of ritual impurity the tzitz, the High Priest’s forehead plate, allows to count as valid despite ritual impurity.
