מתני׳ לא יחפור אדם בור סמוך לבורו של חבירו ולא שיח ולא מערה ולא אמת המים ולא נברכת כובסין אא"כ הרחיק מכותל חבירו שלשה טפחים וסד בסיד
MISHNA: A person may not dig a pit close to the pit of another, in order to avoid damaging the latter’s pit. And similarly, one may not dig a ditch, nor a cave, i.e., a covered pit, nor a water channel, nor a launderer’s pond, which is a pit used for washing clothes, unless he distanced all of these three handbreadths from the wall of another and he plasters lime on the place where there is water.
גמ׳ פתח בבור ומסיים בכותל (ליתני אלא אם כן הרחיק מבורו של חבירו ג"ט)
GEMARA: The tanna of the mishna opens by speaking of a pit: A person may not dig a pit close to the pit of another, and yet he ends with a reference to a wall: Unless he distances it from the wall of another. Let the tanna teach: Unless he distanced his pit or ditch three handbreadths from the pit of another, just as he begins his statement by referring to a pit. Why does the mishna suddenly mention a wall here?
אמר אביי ואיתימא רב יהודה מכותל בורו שנינו
Abaye said, and some say it was Rav Yehuda who said: We learned that the mishna means: From the wall of his pit. In other words, one should read the mishna as follows: Unless he distanced his pit or ditch three handbreadths from the wall of another’s pit. The neighbor also built his pit close to the border between the two properties, and the mishna is teaching that the one digging a pit must distance it three handbreadths from the wall of the pit of the other.
וליתני אא"כ הרחיק מבורו של חבירו ג' טפחים הא קמ"ל דכותל בור שלשה טפחים נפקא מינה למקח וממכר כדתניא האומר לחבירו בור וכותליה אני מוכר לך צריך שיהא הכותל שלשה טפחים
The Gemara challenges: But even so, let it teach: Unless he distanced his excavations three handbreadths from the pit of another, and one would understand that the term pit is referring to the wall of the other’s pit. The Gemara responds: By using the phrase: From the wall of another, this teaches us incidentally that the wall of a pit must be at least three handbreadths thick, as the wall of the other’s pit occupied the full three handbreadths between the cavity of his pit and the property of his neighbor. The practical difference of this observation is with regard to buying and selling, as it is taught in a baraita: With regard to one who says to another: I am selling you a pit and its walls, the wall of the pit must be at least three handbreadths thick.
א"ל רב יימר לרב אשי לאו דכתב רחמנא במשקלות למה לי א"ל לטומן משקלותיו במלח היינו גזל מעליא הוא לעבור עליו משעת עשייה
Rav Yeimar said to Rav Ashi: Why do I need the prohibition that the Merciful One wrote with regard to weights: “You shall do no unrighteousness in judgment, in measure, in weight, or in volume” (Leviticus 19:35)? It is merely another form of robbery. Rav Ashi said to him: It is referring to a seller who buries his weights in salt, in order to lighten them. Rav Yeimar said: That is the same as full-fledged robbery; therefore, it should not require a separate derivation. Rav Ashi answered: It is written to establish that he violates the prohibition from the moment of the act of burying them. He violates the prohibition even before he actually deceives a buyer with the buried weights.