While the Temple was standing, a kohen who had hametz in his possession that he received as teruma (tithes) needed to destroy it before Pesah together with the rest of his hametz. Our Gemara quotes a baraita that brings the teaching of Rabbi Elazar ben Yehuda ish Bartota in the name of Rabbi Yehoshua regarding erev Pesah that falls on Shabbat. In such a case the hametz must be destroyed on Friday, leaving just enough for the Shabbat meal. Rabbi Elazar taught that all hametz should be burned on Friday, including tithes – whether or not they were tahor (ritually pure) – and food for two meals on Shabbat should be left from non-teruma hametz that must be finished before four hours into the day on Shabbat morning.
The baraita records the following conversation that took place in response to Rabbi Elazar’s teaching:
Q. Why should the tithes be burned on Friday? Perhaps we will find kohanim on Shabbat who could have eaten them and it will turn out that the tithes were burned for no reason, which is forbidden?
A. Before burning them we looked for people who could eat the tithes, and did not find anyone.
Q. Perhaps there are such kohanim that slept outside the walls of Jerusalem, and tomorrow they will enter the city?
A. Were we to worry that someone might come tomorrow, then we should also refrain from burning teruma that is a safek (doubt), i.e. that we are unsure about its status since it may have become tameh (ritually defiled), because perhaps Eliyahu ha-Navi will come tomorrow (Shabbat) to herald the arrival of the Messiah, and he will be able to tell us whether the teruma became tameh or not.
They said to him: That possibility is no source of concern, as the Jewish people have already been assured that Elijah will come neither on a Friday nor on the eve of a Festival, due to the exertion involved preparing for the upcoming holy day. Consequently, Elijah will certainly come neither on Friday, nor on itself, which is Passover eve.
According to tradition, Eliyahu will not come to rule with regard to questions of halakha. Nevertheless, the case of teruma that may have become tameh can be resolved by Eliyahu because it is a question of establishing the facts in a specific case, not a question of establishing a halakhic ruling.
While the baraita discusses whether or not it is appropriate to burn teruma on the day before erev Pesah, it does not deal directly with the question of burning regular hametz (hullin). According to many rishonim the conclusion that needs to be reached is obvious – if we can burn teruma, then we can certainly burn hullin. Some argue, however, that we are allowed to burn the teruma only because it is available solely to a limited number of people – namely, kohanim – to eat. Hullin, however, can be eaten by anyone, so it is likely that someone will come tomorrow who would be willing to eat the hametz. Therefore we should not destroy it until the latest possible time.