A person checked a certain barrel of wine so that he could use it to (gradually) declare it as the Terumah for other wine in his possession. He later came back and discovered that it had soured, thereby disqualifying it from being Terumah for his wine. For the first 3 days after his original check, he can certainly assume that the wine was still fine. After that, it is doubtful whether it had already soured.

R. Simon citing R. Yehoshua ben Levi: If he separated during the first three days after his original check, it is certainly Terumah; the last three days it was certainly vinegar; the period in between is doubtful.

R. Abahu: I heard it from R. Yehoshua ben Levi, but what can I do, as R. Yochanan said that for the first 3 days after his original check, he can certainly assume that the wine was still fine; but any time after that, it is doubtful.

R. Ila citing R. Elazar/ R. Yasa citing Rabbanan who heard in Ben Itian's Beis Midrash: R. Yehoshua ben Levi's rule also applies in the case of a lost tamei needle, if he came later and found it to be rusty. (A needle is a vessel and can become tamei, unless it is rusty because it has become unusable). If a needle was found in meat and it is currently rusty, are we concerned that it had fallen there when it had not been rusty and the meat then contracted tumah from it, or not?)

R. Simon citing R. Yehoshua ben Levi: If he found it during the first three days after it was lost, it is certainly tamei; if he found it after a longer period of time, it is assumed that for the last three days it was already rusty and the meat is tahor; the period in between is doubtful.

R. Abahu: I heard this (also) from R. Yehoshua ben Levi, but what can I do, as R. Yochanan said that for the first 3 days after he lost it, he must certainly assume that the meat is tamei, as the needle was not yet rusty; more than three days, it is doubtful.