Tractate Nedarim, Mishnah 8. This mishnah deals with a condition attached to a vow involving a time limit, and with the difference between two formulations that are nearly identical in their wording yet differ in their law.
The first formulation - "she'at osah eini ochel ad haPesach":
The mishnah says: "she'at osah eini ochel ad haPesach" - "that which you make, I will not eat until Pesach," and likewise "she'at osah eini miskaseh ad haPesach" - "that which you make, I will not wear until Pesach." The husband forbids himself to eat from his wife's handiwork, and also to cover himself and dress in garments that she makes, until Pesach.
"Asta lifnei haPesach" - even if she prepared the item before Pesach, the prohibition takes effect on him from the moment he made the vow, and he may not eat it or wear it until Pesach. However, "mutar lo lochal ulehiskasos le'achar haPesach" - he is permitted to eat it and to wear it after Pesach, since he forbade it upon himself only until Pesach. The fact that she made and produced the item before Pesach makes no difference at all: the duration of the prohibition was set as lasting until Pesach.
The second formulation - "she'at osah ad haPesach eini ochel":
But if he said: "she'at osah ad haPesach eini ochel" - "that which you make until Pesach, I will not eat," or "she'at osah ad haPesach eini miskaseh" - "that which you make until Pesach, I will not wear" - here the time element does not limit the duration of the prohibition, but rather defines which items are forbidden: whatever she makes until Pesach he has forbidden upon himself forever.
Therefore, "asta ad shehigia haPesach" - if she prepared the food or the garment before Pesach, he may not eat it or wear it even after Pesach.
In summary: the two formulations differ from one another only in the placement of the words "until Pesach." In the first formulation they limit the time of the prohibition, and therefore after Pesach everything is permitted, even what was made beforehand. In the second formulation they define which items were included in the vow, and therefore whatever was made until Pesach remains forbidden to him even afterward.