One who has had a seminal emission while sleeping on Yom Kippur must immerse himself in the ritual bath to purify his body from the impurity of the semen he emitted. In the words of the early sages (Tanaaim): “One who has a seminal emission on Yom Kippur immerses and in the evening he rubs.” This means that in the evening he cleans his dirty body so
the dirt will not serve as separation between his body and the bath waters. The scholars asked: what is the point of cleaning the dirt off after the immersion? Answer: The early sages, in saying that he should cleanse himself in the evening, meant the evening of Yom Kippur; he should cleanse himself before the holiday lest he have a seminal emission and need to immerse himself in a ritual bath. The early sages also said that one who has a seminal emission on Yom Kippur will have all his sins forgiven. The scholars ask: Did not the early sages teach us the opposite: “One who has a seminal emission on Yom Kippur will find his sins lined up,” that the sins are lined up before G-d so he may be punished? Answer: His sins are lined up before G-d so that He may forgive the man for them. The early sage Rabbi Ishmael also stated that a seminal emission on Yom Kippur is a sign that G-d wants to punish the man and kill him in the coming year. If the year passes and the man remains alive, it is a sign that he has merited life in the World to Come, for it is testimony that his righteousness has overcome the evil decree. One of the scholars, Rav Nachman son of Isaac, supported this ruling that the man is righteous. On Yom Kippur one is forbidden to have sexual relations, and everyone desires sex but cannot fulfill their desires. One who has had a seminal emission during the night has fulfilled his desires yet has not been punished with death, meaning that he is completely righteous.
Another scholar, Rav Dimi, said that one who has had a seminal emission on Yom Kippur will merit having many children.
(Babylonian Talmud, Tractate Yoma, 85a)