The sixth perek of Massekhet Pesahim focuses on the occasional occurrence of erev Pesah she’hal lehiyot be-Shabbat – when Passover falls out on Sunday and the sacrifice needs to be brought on Shabbat. Which activities are considered essential for the korban Pesah to the extent that they “push aside” the restrictions of Shabbat, and which should be left to be done when Shabbat ends? The Mishna (65b-66a) presents the basic rules (e.g. slaughtering the korban is permitted on Shabbat, but roasting it should be left for after Shabbat), including the general principle taught by Rabbi Akiva, that any melakha that is an essential part of the sacrifice that cannot be done before (or after Shabbat) will, in fact, be permitted.
The Benei Beteira appear to have been the ancestors of a well-known rabbinic family, including, for example, the sage Rabbi Yehuda ben Beteira, who lived several generations after the destruction of the Temple. It appears that this family held a position of national religious and spiritual authority, even though they did not have an official position as did the family of the Nasi. We find that they are consulted on matters of national importance not only during Hillel’s time, but after the destruction of the Temple during Rabbi Yohanan ben Zakai’s time, as well.
Faced with this uncertainty, the Benei Beteira sought out someone who had a tradition about this situation.
They said to them: There is a certain man in Jerusalem who came up from Babylonia, and Hillel the Babylonian is his name. At one point, he served the two most eminent scholars of the generation, Shemaya and Avtalyon, and he certainly knows whether the Paschal lamb overrides or not. The sons of Beteira sent messengers and called for him. They said to him: Do you know whether the Paschal lamb overrides or not? He said to them: Have we but one Paschal lamb during the year that overrides? Do we not have many more than two hundred Paschal lambs, i.e. sacrifices, during the year that override?
Hillel ruled that the Pesah sacrifice is brought on Shabbat, just as the daily korban tamid is brought on Shabbat, by pointing out that a similar word be-mo’ado appears in the Torah with regard to each of them (see 9:2 and 28:2). After Hillel brought the proofs for this ruling, he was immediately given the position of Nasi.
The Jerusalem Talmud asks why this halakha had been forgotten, after all, was it so uncommon to have erev Pesah fall out on Shabbat? Several answers are given to this question:
The answer that appears in the Jerusalem Talmud is that miraculously the two dates had not coincided in years so that Hillel would be given the opportunity to gain prominence.
Another approach suggests that the years of Sadducee control of the Temple left many areas of Jewish law in question.