Before us is mishnah 8 in chapter 6 of Tractate Nedarim, which deals with the question of whether someone who vows against a particular fruit is also forbidden in the by-products made from it.
The words of the mishnah:
"Hanoder min hatemarim - mutar bidvash temarim" - one who vowed not to eat dates is permitted to have date honey, since it is merely a by-product.
"Min hasitvaniyot - mutar b'chometz sitvaniyot" - sitvaniyot are late grapes of the end of autumn and winter, which are not particularly fit for eating. One who vows against them is permitted the vinegar made from them, just as in the case of dates: the vow applies only to the item itself and not to its by-products.
The opinion of Rabbi Yehudah ben Beseira:
Rabbi Yehudah ben Beseira disagrees and rules: "Kol sheshem toladto keruyah alav v'noder heimenu - asur af b'toldotav" - anything that carries the name of the thing that produced it, that is, the thing from which it came, such as date honey and sitvaniyot vinegar, then when a person vows against the item itself (against dates or against sitvaniyot) he is forbidden in the by-product as well, since the by-product carries with it the name of the original item.
"V'hachachamim matirin" - what are their words referring to?
The Gemara clarifies what this ruling refers to, and concludes that the words of the Sages refer to one who vows against sitvaniyot, those late grapes, regarding which the first Tanna holds that he is forbidden in the grapes themselves and permitted in the vinegar made from them.
The Sages disagree with this and hold the opposite: the sitvaniyot themselves are permitted, since they are not really fit for eating, while the vinegar is forbidden, because the intention of the one who vowed is directed specifically at the by-product, which is the more edible of the two: the original fruit is not particularly fit for eating, while sitvaniyot vinegar is more fit. It turns out that the "permit" stated by the Sages refers to the sitvaniyot themselves, while sitvaniyot vinegar is in fact forbidden.
However, in the case of one who vows against dates, even the Sages agree that the dates are forbidden and the date honey is permitted, since the dates themselves are fit for eating. On this point the Sages agree with the first Tanna.
In summary: in this mishnah the Tannaim disagree about the law of one who vows against a fruit with regard to its by-products. According to the first Tanna the vow applies only to the item itself, and therefore one who vows against dates is permitted date honey and one who vows against sitvaniyot is permitted sitvaniyot vinegar. Rabbi Yehudah ben Beseira forbids the derivatives as well, since the name of the source is called upon them. And the Sages, as the Gemara explained, permit the sitvaniyot themselves, which are not fit for eating, and forbid the vinegar, because the intention of the one who vowed is directed at it, while regarding dates they agree with the first Tanna.