I took a vow that if Allaah, the Exalted, blessed me with money, I would to give part of it in charity. I was blessed with money, but I am in dire need of it. Can I give only one-fourth of the vowed money and thus not bear any sin (for breaking my vow), or should I give the whole vowed money in charity even if it constitutes harm to me?

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.

Taking conditional vows is disliked in Islam because it is just a means whereby wealth is taken from the miserly person. However, if a person took a conditional vow, then it is incumbent on him to fulfill it in the same manner as he had vowed once its condition is fulfilled (i.e. the thing upon which the vow-taker conditioned his vow takes place). It is impermissible for him to change his vow, offer anything other than the vowed object, or cancel his vow. This is because Allaah, the Exalted, says (what means): {(Then let them) … and fulfill their vows...} [Quran 22:29] Moreover, the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever vowed to do an act of obedience towards Allaah, the Exalted, must do it..." [Al-Bukhari and others]

Hence, you are required to give the complete vowed portion of the money in charity. Offering only one-fourth or part of the vowed money will not clear you of your liability of the vow.

Allaah Knows best.