1. One can be חייב both for כניסה and for פרישה if his wife became a niddah during תשמיש

The Mishnah on Daf 14b taught that if one’s wife became a niddah during relations, ופירש מיד – and he withdrew immediately (without waiting for his arousal to abate), he is liable for a korban, מפני שיציאתו הנאה לו כביאתו – because his leaving is pleasurable to him like his entry. On the previous Daf, Abaye said such a person would be liable to two korbanos, one for the כניסה – entry into relations during which she became a niddah, and one for the פרישה – withdrawal. Rava proves that this must have occurred סמוך לוסתה – close to her anticipated niddah period. Therefore, it is not an אונס that she became a niddah during תשמיש, but a שוגג, for mistakenly thinking she would remain tahor the entire תשמיש. The case is one who knew that relations סמוך לוסתה are prohibited but was unaware of the prohibition against immediate פרישה when she becomes a niddah; therefore, the two mistakes are independent and obligate separate korbanos. Rava proves each of these korban liabilities from Mishnayos.

1. The source, punishment and reward for abstaining סמוך לוסתה

A Baraisa quotes the passuk: והזרתם את בני ישראל מטומאתם – you shall separate the Children of Yisroel from their contamination. Rebbe Yoshiyah said: מיכן אזהרה לבני ישראל – from here is a warning to the Children of Yisroel, שיפרשו מנשותיהן סמוך לוסתן – that they should separate from their wives close to their anticipated period. Rabbah says one must separate an עונה – a time period before, i.e., the full daytime of nighttime before. Rebbe Shimon bar Yochai said that if one does not separate from his wife close to her anticipated period, אפילו הויין לו בנים כבני אהרן מתים – even if he has sons like Aharon’s sons, they will die, because the above passuk is written near "אחרי מות" – after the death of (Aharon’s sons). Rebbe Yochanan said that anyone who does separate from his wife סמוך לוסתה will merit male children. Rebbe Yehoshua ben Levi says he will merit בנים ראויין להוראה – children worthy of issuing rulings. These two statements were also made about one who makes הבדלה on wine on מוצאי שבת.

1. If one must know how he became tamei, vs. knowing one’s specific transgression for a korban

In the Mishnah on Daf 14b, Rebbe Eliezer and Rebbe Akiva each say that one is only liable for forgotten tumah, but not for forgetting about the Mikdash (in opposition to the Tanna Kamma). Chizkiyah says Rebbe Eliezer and Rebbe Akiva disagree with each other where it is unknown how one became tamei. Rebbe Eliezer holds: בעינן עד דידע אי בשרץ איטמי אי בנבלה איטמי – we require that he knew if he became tamei through a sheretz or a neveilah to be liable, but Rebbe Akiva holds כיון דידע דאיטמא בעולם – since he knew he became tamei somehow, he is liable even without knowing the precise source of his tumah.

Ulla posed a contradiction in Rebbe Eliezer, who said that if one ate something which he discovered later was either חלב or נותר, he is liable to a korban, since either one obligates a korban. [Rebbe Yehoshua holds one is not liable עד שיודע לך במה חטא – unless it is known to you with what prohibition you sinned.] Ulla answers that each law emerges from the language of its respective passuk. Later, Rebbe Yochanan says there is no practical argument between Rebbe Eliezer and Rebbe Akiva.

Siman - Chuppah (בן י"ח לחופה ). At the chuppah in the hall where the כניסה entrance and the פרישהexit were the same door, the Rabbi gave a berachah that the chosson should be zocheh to have male children fitting to issue rulings, like the Dayan sitting in front who was being asked if one needs to know how he became tamei to be chayav a korban.