I vowed to give a thousand dinars from the money of the company that I manage with my brothers if a certain deal was concluded. Praise be to Allah Almighty, the deal was actually concluded. Nevertheless, when I told my brothers about the vow that I had taken, they told me that they had nothing to do with it! What should I do? Can I offer the vow in installments? Moreover, there is a sum of a thousand dinars that is due upon my father, and the company will pay it. May I intend that this sum is the fulfillment of the 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, sallallaahu ‘alayhi wa sallam, is His slave and messenger.

Vowing is disliked because it was authentically narrated that the Prophet, sallallaahu ‘alayhi wa sallam, forbade it. Whoever vows to obey Allaah Almighty should fulfill his vow because the Prophet, sallallaahu ‘alayhi wa sallam, said: “If one vows to obey Allaah Almighty, then he should obey Him, and if one vows to disobey Allaah Almighty, then he should not disobey Him.” [Al-Bukhari and others]

Your vow is considered a conditional vow as it is contingent upon the fulfillment of a certain condition. Once this condition is achieved it is obligatory to fulfill the vow. Fulfilling the vow is obligatory upon you alone. You should pay its value from your own wealth because you are the one who took the vow. It is not obligatory upon your brothers to fulfill it, and you do not have the right to commit them to this. There is no harm in offering the vow in installments if you did not vow to give it all at once.

If the company will repay the debt of your father, then he has found a repayment for his debt. Therefore, he is not considered incapable of repaying it. Based on this, it does not clear you of your liability of the vow if you offer it as a fulfillment of your vow. You may not consider the money paid by the company for repaying the debt as a fulfillment of the vow either since your brothers have previously refused to take part in fulfilling your vow from the money of the company. 

Allaah Knows best.