Reference for Eduyot 7:3
הֵעִיד רַבִּי צָדוֹק עַל זוֹחֲלִין שֶׁרַבּוּ עַל הַנּוֹטְפִים, שֶׁהֵם כְּשֵׁרִים. מַעֲשֶׂה הָיָה בְּבִירַת הַפִּלְיָא, וּבָא מַעֲשֶׂה לִפְנֵי חֲכָמִים וְהִכְשִׁירוּהוּ:
R. Tzaddok testified — that they are kosher — about running waters [zochalin viz. (Deuteronomy 32:24): "zochalei afar" ("the 'crawlers' in the dust"), which, halachically, are equivalent to a well, which purifies with any amount of running water, and which are kosher for the consecration of the waters of the sin-offering (the red heifer) and for the immersion of zavim], which (zochalin) (intermixed with and) "outnumbered" the notfim ["dripping waters," like rain water, which, halachically, is like a mikveh, which purifies, with forty sa'ah and in an eshboren (a water collection pit), and which are unfit for the consecration of the waters of the sin-offering, not being "living waters," and likewise, for the immersion of zavim — When the running waters have mixed with the dripping waters and "outnumbered" the dripping waters, they are halachically like running waters and are kosher for the consecration of the waters of purification (of the red heifer) and for the immersion of zavim, and they cleanse, as running waters do, with any amount.] It (such an "outnumbering") once occurred in Biryath Hapilya, and they brought it to the attention of the sages, who pronounced them (the waters) kosher.