Taanit 6B

הנודר עד הגשמים ⁠— משירדו גשמים עד שתרד רביעה שניה.

In the case of one who vows to prohibit from himself a type of benefit until the rains, the vow is in effect from when the rains begin to fall until the second rainfall, as this is considered the time of the rains.

רב זביד אמר: לזיתים. דתנן: מאימתי כל אדם מותרין בלקט בשכחה ובפאה ⁠— משילכו הנמושות. בפרט ובעוללות ⁠— משילכו עניים בכרם ויבואו. בזיתים ⁠— משתרד רביעה שניה.

Rav Zevid said: The time of the second rainfall is also significant with regard to a halakha that deals with olives, as we learned in a Mishnah: From when is any person permitted to collect gleanings, forgotten sheaves, and pe’a, produce of the corners of a field, which may normally be taken only by the poor? Any individual is permitted to collect them only from when the searchers [namoshot], the last of the poor to arrive, have left the field. From when may anyone collect yield of the vineyard in the case of the single grapes and small, incompletely formed clusters of grapes, likewise reserved for the poor? From when the poor have left the vineyard and come back after the second time, an indication that they have collected all that they wish. From when may anyone collect yield of the trees in the case of forgotten olives? From when the second rainfall falls.

מאי ״נמושות״? אמר רבי יוחנן: סבי דאזלי אתיגרא. ריש לקיש אמר: לקוטי בתר לקוטי.

Incidentally, the Talmud asks: What is the meaning of the term for searchers, namoshot? R' Yoḥanan said: It is referring to elders who walk with a staff [atigra]. Since they walk very slowly, they certainly see everything they wish to collect. Reish Lakish said: It is referring to the gleaners who come after all the gleaners, i.e., who arrive after two rounds of the poor have passed through the field.