I vowed to Allah, the Exalted, to fast the three white days (the 13th, 14th and 15th of each lunar month) throughout my entire life, if He fulfilled my wish. Allah Almighty actually fulfilled my wish. I set some conditions for the vowed fasting. I stipulated that I would fast on the three white days, every month, unless I am expecting guests, throwing a banquet, my husband has those days off, something unexpected happens and prevents me from fasting, or when I am invited over to a relative's house. My husband was angry at me because I made such a vow without seeking his permission. I am confused and do not know whether to obey my husband or fulfill my vow.

All perfect praise be to Allaah, The Lord of the Worlds. I testify that there is none worthy of worship except Allaah, and that Muhammad is His Slave and Messenger.

When a person vows to carry out an act of obedience to Allaah, the Exalted, and puts the occurrence of a particular thing as a condition for his vow, then he is obliged to fulfill it when that thing takes place. The Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever vowed to offer an act of obedience to Allaah, the Exalted, must do it..." [Al-Bukhari, Abu Daawood, An-Nasaa‘i, At-Tirmithi and Ibn Maajah]

Scholars refer to this vow as conditional vow; whenever the condition is fulfilled (i.e. the thing upon which the vow-taker conditioned his vow takes place), he is obliged to fulfill his vow.

Al-Buhooti said: "If the vow-taker says, 'If Allaah, the Exalted, blesses my patient with recovery or returned my lost property to me, then I would perform such-and-such prayers or fast such-and-such days', then when this condition is fulfilled, he is obliged to fulfill his vow." [Ar-Rawdh Al-Murbi‘]

Now, as the questioner says that her husband did not give her permission to make this vow, she is not required to do anything regarding her vow based on a condition that she has stipulated; namely, the condition that states that she will not fast if something unexpected happens and prevents her from fasting. This is so because her husband's refusal to let her fast is included in the meaning of the aforementioned condition. Nevertheless, she has to resume the fulfillment of her vow whenever her husband gives her permission to fast and when there are no other impediments preventing her from fasting. However, if she intends a specific hindrance by this condition and not any impediment. Then, whenever her husband forbids her from fasting any of the vowed days, she should obey him and abstain from fasting. This is because the wife's obedience to her husband should be given precedence over the fulfillment of her vow. In that case, she has to make up for that day, and no expiation is due on her because she has a valid excuse for not fasting. According to one of the two scholarly views in this regard, it would be better if she offers an expiation. Ibn Qudaamah said, about the one who vows to fast a particular day and missed it: "If the vow-taker did not fast the vowed day due to a valid excuse, then he is obliged to make up for it because it is obligatory on him just like the fasting of Ramadan. There are two scholarly opinions regarding whether the vow-taker is obliged to offer an expiation in this case or not. One opinion suggests that he is obliged to offer an expiation for delaying the fulfillment of the vow, while the other suggests that it is not incumbent upon him to offer an expiation because he delayed fulfilling the vow for a valid excuse, just like one may delay the fasting of Ramadan due to a valid excuse." [Ash-Sharh Al-Kabeer]

The important point, here, is that whenever the hindrance preventing the questioner from fasting ceases to exist, she should fast the vowed days. The expiation for breaking an oath is: to free a believing slave; to feed ten needy people: each should be given half a Saa‘ (equivalent of 1.5 Kg) of wheat, rice, or the like of the  standard food of the country; or to offer them clothing. If she fails to apply any of these options, then she should fast three days.

Allaah Knows best.