Reference for Keritot 37:23

(ויקרא ד, כג) או הודע אליו חטאתו אי אית ליה ידיעה הוא דמחייב

<big><b>MISHNAH: </b></big>[IF BOTH] HELEB AND NOTHAR LAY BEFORE A PERSON AND HE ATE ONE OF THEM BUT DOES NOT KNOW WHICH, OR IF HIS MENSTRUANT WIFE AND HIS SISTER WERE WITH HIM IN HIS HOUSE AND HE UNITED, IN ERROR,<span class="x" onmousemove="('comment',' I.e., thinking it was his wife and that she was clean. In all these instances the fact that he committed a trespass is afterwards established beyond doubt, though the transgressor was unaware of it at the time of action, but it is unknown which law was broken.');">⁹</span>

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