Talmud for Chagigah 1:8
הֶתֵּר נְדָרִים פּוֹרְחִין בָּאֲוִיר, וְאֵין לָהֶם עַל מַה שֶּׁיִּסְמֹכוּ. הִלְכוֹת שַׁבָּת, חֲגִיגוֹת וְהַמְּעִילוֹת, הֲרֵי הֵם כַּהֲרָרִים הַתְּלוּיִין בְּשַׂעֲרָה, שֶׁהֵן מִקְרָא מֻעָט וַהֲלָכוֹת מְרֻבּוֹת. הַדִּינִין וְהָעֲבוֹדוֹת, הַטָּהֳרוֹת וְהַטֻּמְאוֹת וַעֲרָיוֹת, יֵשׁ לָהֶן עַל מַה שֶּׁיִּסְמֹכוּ. הֵן הֵן גּוּפֵי תּוֹרָה:
The absolution of vows "flies in the air," there being no (Scriptural) support for it. [i.e., There is only a slight allusion in Scripture to a sage's being able to absolve one of his vow, and it (in itself) is not to be relied upon. But thus was it handed down to the sages through the oral tradition (i.e., that they are thus empowered)]. The laws of Shabbath, of the festival offerings, and of me'iloth (abuse of consecrated objects) are like "mountains hanging by a hair" [There are halachoth among them which hang on only a slight Scriptural allusion, like a mountain hanging by a hair of one's head], having few Scriptural referents, yet embracing a great body of halachoth. Laws (monetary laws), the sacrificial service, (the laws of) purity and impurity, and (the laws of) illicit relations have what to rely on (in Scripture). Both are essentials of Torah. [The gemara explains: "Both these and these are essentials of Torah." That is: Both those which have no (Scriptural) support and those which do. Both those which are like "mountains hanging by a hair, etc." — all are essentials of Torah.]