Reference for Chullin 66:23

דלמא כי קאמר רבי עקיבא הני מילי בתרומה וקדשים דחמירי אבל לחולין שניות הויין

only with regard to terumah or consecrated food, since these are to be treated with strictness, but with regard to common food [he would agree that] they are unclean only in the second degree.

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