Bava Batra 18A

המלח, ואת הסיד, ואת הסלעים מכותלו של חבירו שלשה טפחים, או סד בסיד. טעמא דאיכא כותל, הא ליכא כותל ⁠– סומך!

salt, and lime, and rocks 3 handbreadths from the wall of another, or he can plaster the wall with lime. The Talmud analyzes this statement: The reason for this ruling is that there is a wall there belonging to his neighbor, from which it may be inferred that if there is no wall there, one may place these substances close to the boundary of his neighbor’s courtyard. This presents a difficulty for the opinion of Rava according to the first version of the dispute, which states that one may not place these substances close to a boundary even in the case of a field that is not designated for pits.

לא; כי ליכא כותל נמי לא סמיך. ואלא מאי קא משמע לן? הא קא משמע לן ⁠– דהני קשו לכותל.

The Talmud rejects this proof: No, even if there is no wall one may also not place these substances close to the boundary. The Talmud asks: Rather, what does mentioning a wall here teach us? The Talmud answers: This teaches us that all these substances are damaging to a wall.

תא שמע: מרחיקים את הזרעים, ואת המחרישה, ואת מי רגלים מן הכותל שלשה טפחים. טעמא דאיכא כותל, הא ליכא כותל ⁠– סמיך! לא; כי ליכא כותל נמי לא סמיך. ואלא מאי קא משמע לן? הא קא משמע לן ⁠– דמתונתא קשה לכותל.

The Talmud suggests: Come and hear another proof from the Mishnah: One must distance seeds, and the plow, and urine 3 handbreadths from the wall of another. The Talmud analyzes this ruling: The reason for this ruling is that there is a wall, from which it may be inferred that if there is no wall, one may place these substances close to the boundary of the field. The Talmud rejects this proof as well: No, even if there is no wall, one may also not place these substances close by the boundary. The Talmud asks: But rather, what does this teach us? The Talmud answers: This teaches us that dampness [dimtunta] is damaging to a wall.