Sukkah 34A

אבא שאול אומר: ״ערבי״⁠ — שתים. אחת ללולב, ואחת למקדש.

Abba Shaul says: “Willows” in the plural teaches that there are two mitzvot that involve use of the willow branch. One is the willow branch for the lulav, and one is the willow branch taken for the Temple, with which the people would circle the altar on Sukkot.

ורבנן, למקדש מנא להו? הלכתא גמירי להו. דאמר רבי אסי אמר רבי יוחנן: עשר נטיעות, ערבה וניסוך המים ⁠— הלכה למשה מסיני.

And the Rabbis, who do not interpret the verse that way, from where do they derive the mitzva of the willow branch for the Temple? It is a halakha transmitted to Moses from Sinai that they learned through tradition and not from a verse, as R' Asi said that R' Yoḥanan said: There are 3 halakhot for which the rabbis unsuccessfully sought a Torah source. The first is the halakha of 10 saplings. There is a mitzva by Torah law to extend the sanctity of the Sabbatical Year and to begin refraining from plowing 30 days before the Sabbatical Year begins. However, one may plow around individual saplings to sustain them. In a field that is one beit se’a, 50 by 50 cubits, in which there are 10 evenly spaced saplings, it is permitted to plow the entire field until the onset of the Sabbatical Year to sustain the saplings. The second halakha is the mitzva of the willow branch in the Temple. And the third halakha is the mitzva of the water libation on the altar, which accompanies the daily offerings each day of Sukkot, together with the daily wine libation. No Torah source was found for these halakhot, as each is a halakha transmitted to Moses from Sinai.