Reference for Keritot 36:50
סיפא רבי רישא רבנן
For it was taught: If there were two roads, one unclean and the other clean,<span class="x" onmousemove="('comment',' It is not established which is the unclean road. The uncleanness was so situated in the road that a person passing through it perforce became unclean and therefore unfit to enter the sacred precincts of the Temple. In the first and third instances he is liable, because after the second act there is no doubt that he entered the Temple precincts in a state of uncleanness. In connection with the law concerning the defilement of Temple precincts it is an essential condition that the offender had at one time been aware of his uncleanness, though unconscious of it at the time of entering the Temple precincts. In these two cases there was a moment when he was in no doubt as to his state of certain uncleanness. He is therefore liable to an offering.');"><sup>31</sup></span>