Kiddushin 15A

ואידך? ההיא ⁠– לגזירה שוה הוא דאתא. דתניא, רבי אליעזר אומר: מנין לרציעה שהיא באזן ימנית? נאמר כאן: ״אזן״, ונאמר להלן: ״אזן״. מה להלן ימין ⁠– אף כאן ימין.

And the other Sage, R' Elazar, would say: That term, “his ear,” comes for a verbal analogy. As it is taught in a baraita that R' Eliezer says: From where is it derived that the piercing of a Hebrew slave’s ear with an awl is performed on the right ear? It is stated: Ear, here, with regard to a Hebrew slave, and it is stated there, with regard to the ritual purification of a metzora: “The right ear of he who is to be purified” (Leviticus 14:14). Just as there, with regard to a metzora, it specifies the right ear explicitly, so too here, the piercing of a slave must be performed on the right ear.

ואידך? אם כן לימא קרא ״אזן״, מאי ״אזנו״?

The Talmud asks: And how does the other Sage, the first tanna, derive that this piercing can be performed only on the right ear? The Talmud answers: He would argue that if it is so that the word “ear” is stated only for the sake of the verbal analogy, let the verse say merely: Ear, and one would learn the halakha through a verbal analogy from the case of the metzora’s ear. What is the reason that it states “his ear”? This serves to teach that one who sells himself may not be pierced.

ואידך? ההוא מיבעי ליה: ״אזנו״⁠ – ולא אזנה. ואידך? נפקא לה מ״ואם יאמר העבד״⁠ – העבד ולא אמה.

And the other Sage, R' Elazar, would answer: That formulation is necessary to teach that the mitzva of piercing applies to “his ear” but not her ear. He learns from the pronoun that piercing may be performed only on a male slave, not a female slave. The Talmud asks: And from where does the other Sage, the first tanna, derive this halakha? The Talmud answers: He derives it from the verse: “But if the slave should say” (Exodus 21:5). This indicates that piercing applies to the slave but not to a female slave.