Mishnayos Yadayim Perek 3 Mishnah 2

כל הפוסל את התרומה – that is second degree ritual impurity (i.e., food that became ritually impure through contact with first degree ritual impurity. It renders Terumah/heave-offering with third degree ritual impurity. The Sages decreed that sacred books/scrolls and unwashed hands have second degree ritual impurity status).

מטמאה את חברתה – Whomever had one hand impure and it came in contact with his other pure hand, it becomes defiled, and both of them returned ritually impure.

והלא כתבי הקודש – that they (i.e., the Rabbis) decreed that they (i.e., sacred books/scrolls) are second degree ritual impurity and they invalidate the heave-offering/Terumah (i.e., priest’s due), and they defile the hands that come in contact with them to be second [degree ritually impure], so we see that something second degree ritually impure makes [something else] second [degree ritually impure].

ולא דברי סופרים מדברי סופרים – but the defilement of the hands of all of the defilements, is from the words of the Scribes (i.e., Rabbinic law – generally from the period of Ezra), for Shlomo (i.e., King Solomon) established [the laws of] Eruvin/Sabbath limits and hands [which are not found in the Written Torah]. And Holy Writ that defiles the hands is also from the words of the Scribes, which is from the eighteen matters (i.e., actually decrees) that they made on that day (i.e., when Rabban Gamaliel was deposed: see Talmud Berakhot 28a). But we do not judge/make a ruling from this case to that one to state that just as we found that Holy Scrolls that are second [degree of ritual impurity] make [something else] second [degree of ritual impurity], so here also in the remainder of the defilements that will be that something second [degree ritual impurity] will make [something else] second [degree ritual impurity, for what was established was established was established [and] what was not established was not established. But the Halakha is not according to Rabbi Yehoshua.