Reference for Zevachim 76:2

והאיכא שירים שירים לא מעכבי

It was taught: R. Eliezer b. Jacob said: Beth Shammai maintain [that] two applications in the case of the sin-offering and one in the case of all [other] sacrifices permit [them for consumption] and may render them piggul; Beth Hillel rule: One application [only] in the case of a sin-offering and one in the case of all [other] sacrifices permit [them for consumption] and may render them piggul. To this R. Oshaia demurred: If so, this [controversy] should be recited among the lenient rulings of Beth Shammai and the stricter rulings of Beth Hillel? - Said Raba to him: When the question was [first] asked, it was whether [the sacrifice] was permitted, so that Beth Shammai were stricter.

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