Yevamot 93A

קונם שאני עושה לפיך ⁠— אין צריך להפר.

If a wife said: Konam, i.e., this is forbidden like consecrated property, in reference to anything that I will prepare for your mouth, that is, the payment for any work I perform should be forbidden to you, he is not required to nullify the vow, as it is automatically void, since she was under a prior obligation to give him her earnings as part of their marriage agreement.

רבי עקיבא אומר: יפר, שמא תעדיף עליו יותר מן הראוי לו.

R' Akiva says: He should nullify the vow, lest she exceed more than is fitting for him. A husband is entitled only to a certain sum from his wife’s earnings (see Ketubot 64b). If she earns only the sum of money to which he is entitled, the vow certainly does not go into effect. However, she might earn more, in which case the vow would apply with regard to the additional amount. To avoid this scenario, it is preferable for the husband to nullify the vow. This shows that according to the opinion of R' Akiva a vow applies even with regard to an entity that has not yet come into the world. In this case, the entity is the earnings for work she has yet to perform.

הא איתמר עלה: אמר רב הונא בריה דרב יהושע: באומרת: ״יקדשו ידי לעושיהם״, דידים איתנהו בעלמא.

The Talmud refutes this proof: But wasn’t it stated with regard to that Mishnah that Rav Huna, son of Rav Yehoshua, said: This Mishnah is not referring to a woman who renders the earnings for work she has yet to perform forbidden, but to a wife who says: Let my hands be consecrated to their Maker. In other words, she declares that it is as though her hands were sanctified, which means that anything produced by them is forbidden. Since these hands are in the world, she has not attempted to acquire something that does not exist. Therefore, there is no proof from here with regard to R' Akiva’s opinion on that issue.