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.
It is authentically proven that making a vow is disliked in the Sharee'ah. Nevertheless, when one vows to obey Allaah, then he has to fulfill such a vow. It was narrated that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever vowed to obey Allaah should obey Him, and whoever vowed to disobey Him should not do so." [Al-Bukhari and others]
The immediate fulfillment of a vow is not necessary unless its wording implies so. If you are unable to fulfill the vow and pay your debts at the same time, whether they are installments, through borrowed money, or any other such thing, then you are required to pay debts first. Unlike the rights due to Allaah, which are potentially subject to His forgiveness, a right due to a human must be fulfilled, unless he relinquishes it. Consequently, if you cannot fulfill the vow and pay the debt at the same time, then you are allowed to spend all the money that you get for paying all your debts and delay the fulfillment of the vow.
Allaah Knows best.