Reference for Keritot 37:25

הא קמ"ל דר' ישמעאל נמי לא בעי ידיעה בתחלה

AND HE DID FORBIDDEN WORK AT TWILIGHT AND DOES NOT KNOW ON WHICH DAY: R'ELIEZER DECLARES HIM LIABLE TO A SIN-OFFERING, BUT R'JOSHUA DECLARES HIM EXEMPT.

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