She vowed to fast for a month if Allaah caused her husband to mend his ways
Question

                A woman vowed that if Allaah caused her husband to mend his ways and become knowledgeable, she would fast for a month. But until now her husband has not mended his ways. We heard that she has to fast for a month anyway, to discipline herself even if her husband did not mend his ways, because this vow is regarded as a means to get a charitable donation from a miser. What is your opinion, O Shaykh?.
Praise be to Allah.
    Vows are makrooh in principle, and should not be made, 
    because of the report narrated by al-Bukhaari (6608) and Muslim (1639) that 
    Ibn ‘Umar (may Allaah be pleased with him) said: The Prophet  (peace and 
    blessings of Allaah be upon him) forbade vows and said: “They do not avert 
    anything, all they do is get something out of a stingy person.” 

    Al-Bukhaari (6609) narrated from Abu Hurayrah (may Allaah be 
    pleased with him) that the Prophet  (peace and blessings of Allaah be 
    upon him) said: “A vow does not bring the son of Adam anything that I have 
    not decreed for him, but vowing is imposed on him by way of foreordainment. 
    Through vowing I make a miser spend of his wealth.”  

    Although it is makrooh to make vows, it is obligatory to 
    fulfil a vow to do an act of worship, because the Prophet  (peace and 
    blessings of Allaah be upon him) said: “Whoever
    vows to do 
    some act of worship and obedience to Allaah, then let him do it, and whoever
    vows 
    to do some sin, let him not do it.” Narrated by al-Bukhaari (6318). 

    Secondly: 

    Your saying “If Allaah causes my 
    husband to mend his ways and he becomes knowledgeable I will fast for a 
    month” is a vow to do an act of worship, depending on a condition. When the 
    condition is fulfilled, it becomes obligatory to fulfil the vow. If the 
    condition is not fulfilled, you do not have to do anything.  

    Ibn Qudaamah (may Allaah have 
    mercy on him) said concerning vows to do acts of worship and righteous 
    deeds: They are of three types, one of which is doing an act of worship in 
    return for a blessing that is attained or a misfortune that is warded off, 
    such as saying, ‘If Allaah heals me, I must fast for a month’. So the act of 
    worship becomes binding although it is not ordinarily binding, such as 
    fasting, prayer, charity and Hajj. This must be fulfilled according to 
    scholarly consensus. End quote from al-Mughni (13/622). 

    It says in al-Mawsoo’ah 
    al-Fiqhiyyah (12/315): The fuqaha’ are unanimously agreed that it is 
    permissible to make a vow conditional, and it is not obligatory to fulfil it 
    before the condition is fulfilled, because the reason for fulfilling the vow 
    is not present. When the condition is fulfilled, it becomes obligatory to 
    fulfil the vow. End quote. 

    Thus it is clear that what you 
    have heard is not entirely correct. A vow may make a miser give some of his 
    wealth, but the conditional vow does not have to be fulfilled unless the 
    condition is met. 

    It would have been better for you, 
    instead of making a vow, to advise your husband and help him and guide him 
    to pray and do good deeds and seek knowledge, and make a lot of du’aa’ for 
    him. 

    We ask Allaah to help you both to 
    do that which He loves and which pleases Him. 

    And Allaah knows best.