Reference for Niddah 6:8
אמר לו
a dead creeping thing, the objects that were formerly clean are regarded as unclean retrospectively?'<span class="x" onmousemove="('comment',' Lit., 'the former clean are unclean', because it is possible that the creeping thing was in the basket before the objects had been removed and that it consequently imparted uncleanness to the basket from which it was conveyed to the objects. If the creeping thing, it may be added, had been found in the same corner in which the objects were previously kept there could be no question that the latter remain clean, since it may be regarded as certain that they had been removed before the creeping thing had fallen into the basket. For if it had been there earlier it would have been discovered at the time the objects were being removed. ');"><sup>6</sup></span>