Niddah 33 - Cutheans' Purity
If a man emits seed, he becomes ritually impure for that day. In the same vein, if a woman had intercourse and later emitted the man's seed - as long as the seed is viable - she too becomes ritually impure for that day. We learn this from the giving of the Torah. Men were required to separate from their wives for three days in advance. Really, one day would be enough, but since seed remains alive in a woman's womb for three days, we learn from the law about a woman who emits man's seed.
Rami bar Chama asked, "What if a woman emits man's seed while she is counting her pure days, does it ruin her count?" Rava commented, "Because of Rami's sharpness, he asked a meaningless question." However, the Talmud proves that the questions indeed had meaning.
Rav Pappa once came to the city of Tavach. He said, "If there is a smart scholar here, show him to me." One elderly woman said, "We have a scholar, by the name of Rav Shmuel, and you should be like him." Rav Pappa concluded, "If people bless me in his name, he must be truly a God-fearing person."
Rav Shmuel slaughtered an ox for Rav Pappa, and then asked a question about Cutheans's purity that left Rav Pappa perplexed: why are their garments only doubtfully impure, while the garments of an ignoramus are definitely impure? Rav Pappa answered that we are dealing with a Cuthean Sage, but Rav Shmuel pointed out that from the rest of the story it did not look like that.
Art: Domenico Fetti - Portrait Of A Scholar