Kesubos, chapter 7, mishnah 2. The mishnah opens: "HaMadir es ishto shelo tit'am echad mikol haperos" - a man who vowed that his wife should not taste or benefit from a particular kind of fruit.
Who made the vow - the Gemara's explanation:
The Gemara explains that the mishnah does not mean that the husband himself made the vow. Rather, the wife made the vow and the husband upheld it. As is well known, a husband has the right to annul his wife's vow; but if he wants the vow to take effect, this happens in one of two ways:
By explicit ratification: the husband states that he upholds the vow.
By silence: if he did not annul the vow within the first twenty-four hours, the vow takes effect on its own.
"Yotzi v'yiten kesubah":
In such a case the mishnah rules: "Yotzi v'yiten kesubah" - the husband divorces his wife immediately and pays her her kesubah. Why do we not wait thirty days here, as the previous mishnah ruled?
The Gemara explains that the difference lies in how the wife understands what he did:
When the husband himself makes the vow: the wife attributes it to a momentary flash of anger at her, and she does not feel that the marriage cannot succeed. Therefore we wait thirty days.
When the wife makes the vow and the husband upholds it: the wife understands this to mean that her husband hates her, and she cannot live in such a situation. Therefore he must divorce her immediately.
Rabbi Yehudah's view:
Rabbi Yehudah says: "BeYisrael - yom echad yekayem, shnayim yotzi v'yiten kesubah; u'v'chohenes - shnayim yekayem, sheloshah yotzi v'yiten kesubah":
The wife of a Yisrael: for one day he may uphold the vow and keep her with him; on the second day he must divorce her and pay her kesubah.
The wife of a kohen: for two days he may uphold it; on the third day he must divorce her and pay her kesubah.
The reason for the distinction: for the wife of a kohen there is no way back from a divorce - the couple can never remarry each other, and therefore she is given an additional day.
In summary: in this mishnah we learned that "one who vows against his wife" means that the wife made the vow and the husband upheld it - whether by an explicit statement or by remaining silent for twenty-four hours. In such a case he must divorce her immediately and pay her kesubah, without waiting thirty days, because the wife understands his upholding of the vow as hatred and cannot live in such a situation. Rabbi Yehudah sets time limits: one day for the wife of a Yisrael and two days for the wife of a kohen, since the wife of a kohen has no possibility of remarrying her husband after the divorce.