Reference for Chagigah 2:7
בִּגְדֵי עַם הָאָרֶץ מִדְרָס לַפְּרוּשִׁין. בִּגְדֵי פְרוּשִׁין מִדְרָס לְאוֹכְלֵי תְרוּמָה. בִּגְדֵי אוֹכְלֵי תְרוּמָה מִדְרָס לַקֹּדֶשׁ. בִּגְדֵי קֹדֶשׁ מִדְרָס לְחַטָּאת. יוֹסֵף בֶּן יוֹעֶזֶר הָיָה חָסִיד שֶׁבַּכְּהֻנָּה, וְהָיְתָה מִטְפַּחְתּוֹ מִדְרָס לַקֹּדֶשׁ. יוֹחָנָן בֶּן גֻּדְגְּדָא הָיָה אוֹכֵל עַל טָהֳרַת הַקֹּדֶשׁ כָּל יָמָיו, וְהָיְתָה מִטְפַּחְתּוֹ מִדְרָס לַחַטָּאת:
The garments of an unlearned person (am ha'aretz) are midras [av hatumah (proto-uncleanliness) to impart uncleanliness to men and vessels] to perushin (the "guarded"), [who eat their chullin in the cleanliness of chullin] [just as the midras (lit. "the seat") of the zav (one with a genital discharge), which imparts uncleanliness to men and vessels, viz. (Leviticus 15:21): "And whoever touches what she lies upon shall wash his clothes."] The garments of perushin are midras to eaters of terumah. [One level is missing here, viz.: "The garments of perushin are midras to the eaters of second-tithe. The garments of eaters of second-tithe are midras to eaters of terumah," i.e., Cohanim, who eat terumah.] The garments of eaters of terumah are midras to (those who touch) chatath. [All of these levels are ordinances of the scribes, who said that the guarding for cleanliness of one level is not considered guarding vis-à-vis the other. This being so, they decreed that the garments of those on one level be regarded by those on a higher level as if his wife (the wife of the one on the lower level) had sat on them in her niddah time, making them midras of a niddah.] Yosef b. Yoezer was a chasid in the priesthood, notwithstanding which his napkin was (regarded as) midras to (those who ate) kodesh. Yochanan b. Gudgeda ate [chullin] in the cleanliness of kodesh [i.e., as if he were eating kodesh, being heedful of any tumah which would render kodesh unclean], and his napkin was midras to chatath, [but not to kodesh, this tanna holding that chullin prepared in the cleanliness of kodesh is like kodesh. But this is not the halachah. For chullin prepared in the cleanliness of kodesh is not like kodesh in all respects, as stated in the end of Niddah.]