Yevamot 80A

שלא ראה שעה אחת בכשרותו. מנא ידעינן? אמר אביי: כל המטיל מים ואינו עושה כיפה.

who never saw a single hour of life in a state of fitness, as he was born infertile. The Talmud asks: How do we know that one was born this way and was never capable of having children? Abaye said: Anyone who passes water and does not form an arch with his urine, but rather his urine dribbles out downward, never had sexual capacity.

ממאי הואי? דאפיה אימיה בטיהרא ושתיא שיכרא מרקא. אמר רב יוסף: היינו דשמענא לאמי דאמר: ״כל שממעי אמו לקוי״, ולא ידענא מאי ניהו.

Incidentally, the Talmud inquires: From what does this defect arise? What is its cause? The Talmud answers: It results from his mother baking bread at noon and drinking strong beer [shikhra marka] while pregnant. The excessive heating of the mother’s body causes her child to be born with defective reproductive organs. Rav Yosef said: This is the meaning of that which I heard R' Ami say: Anyone who is impaired from his mother’s womb, and at the time I did not know what he was referring to. Now I understand that he was speaking about a man who was infertile from birth.

וליחוש שמא הבריא בינתים! כיון דתחלתו וסופו לקוי ⁠— לא חיישינן.

The Talmud asks: Let us be concerned that perhaps he was cured for some period in the meantime, without our having known about it, in which case he would have had an hour of fitness at some point. The Talmud answers: Since both his beginning and his end are impaired, i.e., he was born with a defect and he presently suffers from the same condition, we are not concerned about such a possibility.

מתיב רב מרי, רבי חנינא בן אנטיגנוס אומר: בודקין אותו שלש פעמים בתוך שמונים יום!

Rav Mari raised an objection from the following Mishnah (Bekhorot 38b): R' Ḥanina ben Antigonus says: One examines a firstborn animal that developed a blemish in its eye 3 times within 80 days to see whether the defect is permanent. This shows that no presumptions are made in such a case; rather, there is concern that the animal may have been cured in the meantime, even if it had the defect at the beginning and at the end of the period.