Moed Katan 4A

שנכנס לשביעית, וקציר של שביעית שיצא למוצאי שביעית.

that entered into the Sabbatical Year, i.e., plowing in the 6th year that will benefit crops growing in the 7th year, and reaping the crops of the Sabbatical Year that continued into the conclusion of the Sabbatical Year, i.e., reaping 7th-year produce that continued to grow into the 8th year.

רבי ישמעאל אומר: מה חריש רשות, אף קציר ⁠— רשות, יצא קציר העומר שהיא מצוה!

R' Yishmael says that this verse is to be understood as referring to Shabbat and not to the Sabbatical Year, in accordance with the straightforward meaning of the verse. It teaches as follows: Just as only optional plowing is prohibited on Shabbat, as there is no instance where plowing fulfills a biblical mitzva, so too, only optional reaping is prohibited, to the exclusion of the reaping of the omer offering, which is a mitzva, and consequently permitted on Shabbat. Nonetheless, the first opinion cited in the baraita, that of R' Akiva, holds that the prohibition against plowing on the eve of the Sabbatical Year is derived from an explicit verse.

אלא אמר רב נחמן בר יצחק: כי גמירי הלכתא ⁠— למישרי ילדה. קראי ⁠— למיסר זקינה.

Rather, Rav Naḥman bar Yitzḥak said: When we learned this as a halakha transmitted to Moses from Sinai, it was to permit plowing in the case of young saplings until Rosh HaShana. In contrast, the verses that were cited come to prohibit plowing in the case of mature and well-rooted trees 30 days before Rosh HaShana of the Sabbatical Year.

וכיון דהלכתא למשרי ילדה, לאו ממילא זקינה אסירה?!

The Talmud asks: But since the halakha transmitted to Moses from Sinai comes to permit plowing in the case of young saplings until Rosh HaShana, does it not automatically follow that in the case of mature trees, plowing is prohibited before Rosh HaShana? Therefore, not only the allowance, but the prohibition as well was learned by tradition as a halakha transmitted to Moses from Sinai, and not from the verses.