We are in Maseches Eduyos, chapter 2, mishnah 1, and before us is the testimony of Rabbi Yehudah ben Bava, who testified about five things.
Rabbi Yehudah ben Bava was a Tanna who lived from the end of the period of the destruction of the Temple until after the Bar Kochba revolt, at the end of which he was killed al kiddush Hashem. He was a student of Shmuel HaKatan, and evidently a particularly great tzaddik. He was even called "chassid," and the Gemara in Bava Kamma says that wherever stories are told about "a certain chassid," the reference is either to Rabbi Yehudah bar Ilai or to Rabbi Yehudah ben Bava. This was an extraordinary man.
The first testimony - "me'ma'anin es haketanos":
We encourage minor girls to perform mi'un (refusal), and particularly in two cases. By way of introduction: on a Torah level a woman becomes betrothed in one of two ways - either she herself accepts her kiddushin, or her father betroths her. Where the girl is an orphan, she cannot be betrothed on her own because she is a minor, nor through her father, since he is no longer alive. The Sages instituted for her benefit, in order to prevent her from being taken advantage of, that her mother or her older brother (from bar mitzvah age) may accept kiddushin on her behalf, and in this way she becomes married on a rabbinic level. The hope is that the husband will protect her from unrestrained behavior.
To dissolve such a marriage, the Sages made the process as easy as possible: it is enough for her to say that she no longer wants this husband, and that is mi'un. Once she has done so, retroactively she was never married at all. That was the entire purpose of this rabbinic institution of marriage - to protect the girl, and if it does not work out well for her, to let her leave it without consequences. A girl who performs mi'un does not receive a kesubah, but since it is as though she was never married, she is even permitted to marry a kohen.
Ordinarily we do not encourage mi'un, since we want the girls to remain married and protected. But in the view of Rabbi Yehudah ben Bava there are two specific cases in which we instruct them to perform mi'un, and both are complex topics in Yevamos chapter 13:
Two brothers who married two sisters: the brothers Reuven and Shimon married the sisters Rachel and Leah. Rachel is married to Reuven in a regular Torah marriage, and Leah is married to Shimon in a rabbinic marriage that can be dissolved through mi'un. Reuven dies childless - Rachel now comes before Shimon for yibum or chalitzah, except that Shimon is already married to her sister Leah, and he cannot perform yibum because of the prohibition of his wife's sister. And if he performs chalitzah with Rachel, Leah becomes the sister of his chalutzah, and he will not be able to remain married to her either. It turns out that Shimon can marry neither Rachel nor Leah, and both sisters will be left without a husband. Therefore, based on a dispute in Yevamos, Rabbi Yehudah ben Bava holds that we instruct the minor to perform mi'un: Leah is going to leave him in any case, and if she performs mi'un, then retroactively she was never married to Shimon at all, and then Shimon will be able to perform yibum with Rachel, build up the house of his brother Reuven, and live with her happily.
Two wives of the deceased brother: Reuven has two wives who are not sisters - an adult married on a Torah level, and a minor married only on a rabbinic level. Reuven dies, and seemingly both come before Shimon for yibum. But if Shimon performs yibum or chalitzah with the minor, that provides no solution for the Torah-level obligation of the adult, who still requires yibum or chalitzah. If, however, he first has relations with the minor, thereby becoming married to her on a rabbinic level, and afterward has relations with the adult - on a Torah level this is a full yibum. It emerges that on a Torah level he has one wife, and on a rabbinic level two wives who cannot live together, since a man may take his yevamah only for the sake of yibum, and that cannot be true of both of them, so he would have to send both of them away. In this situation, where he had relations first with the minor and then with the adult, if the minor performs mi'un - and this is an exceptional case of mi'un, one that undoes a yibum situation, since her actual husband Reuven has already died - then it is as though they were never married, and there is no connection at all between Shimon and the minor. Consequently he will be able to remain married to the adult, who required yibum and with whom he properly performed yibum. Again, since the minor will not remain married in any event, we instruct her to perform mi'un, and in this way everyone, including she herself, can get on with their lives.
The second testimony - "masi'in es ha'ishah al pi ed echad":
This topic appears at the end of Yevamos: a woman may remarry on the strength of the testimony of a single witness who testifies that her husband died. This is a great novelty, since ordinarily a matter of ervah - marriage and divorce - requires two valid witnesses. But the Sages were extremely lenient in order to reduce the problem of agunos. In a case where the husband was overseas and died, we rely on the testimony of a single person, even a slave, even a woman, even a witness quoting another witness, and we permit the widow to marry someone else. Otherwise, she would remain presumed to be a married woman and would be left an agunah who could never remarry.
And why were the Sages so lenient? The answer has two parts:
A matter likely to come to light: there is an assumption that a person does not lie about something whose truth is destined to become clear. If the husband did not really die, he will eventually show up and look for his wife, and the truth will come out.
The severity of the consequences: the Sages imposed exceptionally severe penalties and consequences on a woman who remarried unlawfully while still married to the first husband - regarding mamzerus, regarding the terms of her leaving, and everything that goes with it. Out of fear of the consequences, the widow will be extremely careful to verify that her husband indeed died before she remarries.
The third testimony - "al tarnegol shenniskal biYerushalayim":
A certain rooster in Jerusalem was stoned to death for killing a person. That rooster pecked at the soft spot on an infant's head and killed him, and its punishment was a formal trial and stoning. The basis for this is the verse: "If an ox gores a man or a woman and he dies... the ox shall surely be stoned." Although the Torah speaks of an ox, the law is not limited to oxen alone; it applies to any animal or bird, even a rooster - and that is exactly what happened in practice.
The fourth testimony - "ve'al hayayin ben arba'im yom shenitnasech al gav hamizbe'ach" - wine forty days old that was poured as a libation on the altar:
Wine that is forty days old may be used for the libations in the Beis Hamikdash even initially. The background: one who brings an animal offering, an olah or shelamim, must bring libations along with it, including the wine libation. Ideally one must use actual wine, that is, a beverage that has the power to intoxicate, as it says: "In the holy place shall you pour a libation of strong drink to Hashem" - a libation of something intoxicating. The question is how long grape juice must stand after being pressed before it becomes wine. After the fact, one who used grape juice has fulfilled the obligation, but ideally something intoxicating is required, and this is the threshold the Mishnah establishes: once forty days have passed, it may be used at the outset without any concern.
The fifth testimony - "ve'al tamid shel shachar shekarev be'arba shaos" - the morning tamid that was offered at the fourth hour:
The morning tamid offering was brought four hours into the day, and this refers to a historical event. In the year sixty-five BCE, two brothers, Hyrcanus and Aristobulus, the sons of Queen Shlomtzion and King Alexander Yannai, fought over the kingship in Israel - this is the end of the Chashmonaic period. Yannai was a wicked man, while Queen Shlomtzion was a great woman, and her two sons contended for the crown. Hyrcanus laid siege to Aristobulus, who was inside Jerusalem, in order to capture the city, and even though the two sides were fighting one another, Hyrcanus's side would send up two lambs over the wall each day so that they could be offered.
One time, instead of lambs, goats were sent up, and goats are not valid for the tamid offerings. They were therefore forced to search for lambs, and obtaining them was not easy, until they found two lambs in the courtyard of the Beis Hamikdash in Jerusalem - but this took some time. By the time they offered the morning tamid, its ideal time had already passed, which is before sunrise, between dawn and sunrise. After the fact it may be offered until the fourth hour, and this is the testimony before us.
There is a dispute in Berachos as to whether its time is until four hours or until midday, and many rule like Rabbi Yehudah that its time is only until four hours into the day. From here there is a practical ramification for all of us: the Shacharis prayer corresponds to the morning tamid, and therefore, although ideally one should daven Shacharis at sunrise, which is the ideal time, one may daven it until four hours into the day, close to ten in the morning, depending on the season and location. The basis of this law is the testimony in our Mishnah.
In summary: in this Mishnah Rabbi Yehudah ben Bava testified about five things - that we allow minor girls to perform mi'un in the two cases in Yevamos; that we permit a woman to remarry on the testimony of a single witness, because of the enactment for agunos; that a rooster was stoned in Jerusalem for killing a person; that wine forty days old is valid for libations even at the outset; and that the morning tamid was offered at the fourth hour - from which we learn that the time for Shacharis is until four hours into the day.