Sotah 30A

שלישי הבא מחמת שני, דשני גופיה אסור בחולין ⁠— אינו דין שעושה רביעי בקודש?

whose 3rd-degree impurity came from contact with an item of 2nd-degree impurity, in which case the item with the 2nd-degree impurity is itself forbidden, i.e. impure, even if it is non-sacred food, isn’t it logical to infer that it should be able to impart 4th-degree impurity upon sacrificial food?

וכי תימא משום דאיכא למיפרך: מה לטבול יום שכן אב הטומאה ⁠— הא אייתינה ממחוסר כיפורים, ולא פרכיה!

And if you would say that the reason R' Yosei did not employ this a fortiori inference is because it can be refuted as follows: What is unique about one who immersed that day is that prior to his immersion he was a primary source of impurity, this cannot be, as R' Yosei brought proof for the existence of a 4th degree of impurity from the case of one who has not yet brought an atonement offering, who was also a primary source of impurity prior to his immersion, and R' Yosei clearly did not refute the proof due to this factor. Therefore, the reason R' Yosei did not employ an a fortiori inference from the case of food that contracted impurity from one who immersed that day is clearly that he disagrees with the opinion of Abba Shaul. Consequently, R' Yoḥanan concluded that he cannot understand R' Yosei’s reasoning.

אמר רב אסי אמר רב, ואמרי לה אמר רבה בן איסי אמר רב: רבי מאיר, ורבי יוסי, ורבי יהושע, ורבי אלעזר, ורבי אליעזר ⁠— כולהו סבירא להו דאין שני עושה שלישי בחולין.

§ R' Asi said that Rav said, and some say Rabba ben Isi said that Rav said: R' Meir, and R' Yosei, and R' Yehoshua, and R' Elazar, and R' Eliezer all hold that an item of 2nd-degree ritual impurity status cannot impart 3rd-degree ritual impurity status to non-sacred items. Rav proceeds to prove this by attributing support from the rulings of each of these tanna’im.