Reference for Keritot 37:28

ונעלם ממנו שתי פעמים לחייב על העלם טומאה ועל העלם מקדש

ABOUT ONE WHO DID WORK DURING THE DAY ITSELF BUT HE DID NOT KNOW WHETHER HE DID IT ON THE SABBATH OR ON THE DAY OF ATONEMENT, OR IF HE DID WORK AND DID NOT KNOW WHAT MANNER OF WORK HE DID:<span class="x" onmousemove="('comment',' I.e., he is sure that his work was a forbidden act, but does not remember, e.g., whether he ploughed or sowed.');">¹²</span>

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