Reference for Chullin 257:3

אף לדידי קשיא לי ושאילתיה לרבי אבא בר ממל ואמר לי

Said the other, 'I, too, had this difficulty and I put it to R'Abba B'Memel, and he told me that this ruling was in accordance with R'Meir's view who maintains that covert [contact with] Uncleanness does render unclean'.

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