On the festival of Succot, we gather the daled minim per the Torah’s command: “And you shall take for yourselves… the fruit of the splendid tree (esrog), date palm fronds (lulav), a branch of a braided tree (hadasim) and willows of the brook (Aravot)” (Lev. 23:40). Then, on Hoshana Rabbah the final day of Succot, it is customary to beat the fourth of these daled minim, i.e., the willow branches, on the ground. The details of this “willow-whacking” custom are shrouded in mystery; the Gemara records that the custom existed in the times of the Beit HaMikdash (Sukkah 44b; see Rashi ad. loc.), but precious little has been written on both the origin and meaning of this custom.
However, the text of the tefillah we recite before performing this ritual does include an instructive reference to the “custom of the prophets.” This phrase would seem to suggest that the ritual was instituted by the “prophets”—or, at least, that it is modeled after some practice or ceremony that dates to the era of the prophets. Indeed, in Nevi’im Rishonim, we do find an episode whose central elements correlate with those of the Aravot ritual. Here is the scene, from Sefer Melachim Beit: