Kesubos, chapter five, mishnah 4. The mishnah opens: "HaMakdish ma'aseh yedei ishto - harei zu osah ve'ocheles" - one who consecrates his wife's handiwork, she continues to work and eat from her earnings. If a man consecrates his wife's handiwork, the product she manufactures (for example, a certain quantity of thread she spins from wool), which ordinarily belongs to the husband, the consecration he declared and announced does not take effect, and the wife goes on working and eating from the fruit of her labor.
What case is the mishnah dealing with?
The Gemara explains that this refers to a case in which the wife said, "No support and no handiwork" - meaning: do not provide for me, and I in turn will not give you my handiwork; rather, I will support myself. Under these circumstances she works for herself and eats from what is hers, and therefore her product is not in her husband's possession or under his control, and he has no power to consecrate it.
Our mishnah thus takes the position that the primary obligation rests on the husband to support his wife, and the rabbinic enactment that her handiwork belongs to him was established in exchange for that. It emerges that the arrangement was made from the outset for her benefit - to provide her with support - and in return her handiwork goes to him. Once she chose to waive that and say, "Do not support me, and I will take care of myself," her handiwork does not belong to him, and consequently it is not under his control.
"HaMosar" - the additional work:
The second part of the mishnah deals with the "mosar," the surplus, that is, the additional work the wife does. Later in the chapter we will learn that there is a fixed quantity of product the wife is expected to produce in exchange for the support her husband provides; but anything beyond that is a question: to whom should it go?
The Gemara explains that in addition to her support, the husband is obligated to give his wife a small sum of money on a regular basis, called a "ma'ah kesef," and it is given on a weekly basis. In exchange for that ma'ah kesef, the "mosar" also belongs to him, meaning any additional work she does.
Accordingly, the second part of the mishnah deals with a different case from the first part: the first part speaks of a woman who is not supported by her husband at all, whereas in the second part she does receive her support, but he does not give her the additional ma'ah kesef for her needs. In that case the "mosar" does not go to him.
However, if the wife should pass away in his lifetime, the husband acquires and inherits all the "mosar" that remains. Hence the question the mishnah raises: under these circumstances, when he is destined to inherit it after her death, what is the law if he consecrated that surplus while she was still alive and declared it consecrated - does the consecration take effect? This depends on the fundamental question: can a person consecrate something that has not yet come into the world?
In the words of the mishnah, regarding that additional sum which is not in his possession and will be his only after she passes away: "Rabbi Meir omer: hekdesh; Rabbi Yochanan HaSandlar omer: chullin" - Rabbi Meir says it is consecrated; Rabbi Yochanan HaSandlar says it remains unconsecrated.
Rabbi Meir: a person can consecrate something that is not yet in the world, and therefore the consecration takes effect.
Rabbi Yochanan HaSandlar: a person cannot consecrate something that is not yet in the world, and therefore the consecration does not take effect and the item remains chullin, unconsecrated.
It is worth noting that this very dispute could equally have been stated regarding her handiwork itself, in a situation where she does not receive support, as in the first part of the mishnah. Nevertheless, the Gemara framed the discussion specifically around the "mosar," because of the novelty involved: even with the "mosar," the surplus alone, Rabbi Meir holds that it can be consecrated.
And indeed the law is the same with her handiwork itself: in a situation where the husband does not support her and her handiwork belongs to her, and after her death he will inherit it, Rabbi Meir and Rabbi Yochanan HaSandlar would disagree as to whether a consecration made during her lifetime will be valid in the future.
In summary: in this mishnah we learned that one who consecrates his wife's handiwork in a case where she said, "No support and no handiwork," has not made a valid consecration, since her handiwork is not in his possession. We also examined the "mosar," the work beyond the fixed quantity, which belongs to the husband in exchange for the weekly ma'ah kesef; and where he does not give her that ma'ah, the surplus is not his except after her death by way of inheritance. On that point Rabbi Meir and Rabbi Yochanan HaSandlar disagree regarding the consecration of something that has not yet come into the world.