Sanhedrin 71B

דכוליה קרא יתירא הוא.

since the entire verse is superfluous. The verse’s description of how the father and mother bring their son out appears to be unnecessary, and therefore each element in the verse limits the halakha in a precise manner. When a verse is not superfluous, it is not strictly interpreted.

ומתרין בפני שלשה? למה לי? בתרי סגיא! אמר אביי: הכי קאמר ⁠– מתרין בו בפני שנים, ומלקין אותו בפני שלשה.

§ The Mishnah teaches that after the rebellious son is brought before the elders of the city, he is admonished before 3 people. The Talmud asks: Why do I need him to be admonished before 3 people? Two witnesses should suffice, as in all other matters of halakha. Abaye says: This is what the Mishnah is saying: He is admonished before two people, who serve as witnesses, and he is flogged before 3 people, who constitute a court.

מלקות בבן סורר ומורה היכא כתיבא? כדרבי אבהו, דאמר רבי אבהו: למדנו ״ויסרו״ מ״ויסרו״, ״ויסרו״ מ״בן״, ו״בן״ מ״בן״⁠ – ״והיה אם בן הכות הרשע״.

The Talmud asks: Where is it written that lashes are administered to a stubborn and rebellious son? There is no explicit mention of lashes in the verse. The Talmud answers: It is as R' Abbahu said in another context, as R' Abbahu says: We learned the meaning of the word “chastise” as stated with regard to a defamer: “And the elders of that city should take that man and chastise him” (Deuteronomy 22:18), by means of a verbal analogy from the word “chastise” stated with regard to a rebellious son (Deuteronomy 21:18). And the meaning of the word “chastise” in the latter verse is derived from the word “son” that appears in the same verse. And the meaning of the word “son [ben]” with regard to a rebellious son is derived from the similar word “bin” stated with regard to lashes: “Then it should be if the wicked man deserves [bin] to be flogged” (Deuteronomy 25:2). Consequently, the chastisement mentioned with regard to both a defamer and a rebellious son involves flogging.