Ba'al Keri, A person who had a night pollution

A person from whom semen was emitted during sleep, and as a result, he is required to immerse himself in a ritual bath (mikveh).

("He would stand in prayer and remember that he was a Ba'al Keri; he would not stop but shorten (the prayer) and go down to immerse" - Berakhot 3:5. Similarly: "Proclus son of Plosfus asked Rabban Gamliel in Akko who was bathing in the bathhouse of Aphrodite, 'It is written in your Torah that nothing from the banned item clings to your hand. Why then do you bathe in the bathhouse of Aphrodite?' He said to him... 'If they would give you much money, would you enter idolatrous service naked and Ba'al Keri and urinate before her? And she stands at the entrance of the temple and all the people urinate before her. It is said only of their gods that one who serves them is forbidden because of God, and one who does not serve them is permitted because of God.'" - Avodah Zarah 3:4)

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