Punishment for not fulfilling vows

Firstly: 

Vows are of two types: 

1 – Conditional vows, in
which the vow is dependent upon something happening, as when a person says,
“If Allaah heals me, I will give such and such in charity, or I will fast
such and such a number of days,” and so on. 

2 – Unconditional vows (which are not connected to anything),
such as saying, “I will fast such and such a number of days for Allaah.” 

Both types of vows must be fulfilled, if what is vowed is to
do an act of worship. 

The Prophet (peace and blessings of Allaah be upon him)
said: “Whoever vows to obey Allaah, let him obey Him, and whoever vows to
disobey Him let him not disobey Him.”  

Narrated by al-Bukhaari, 6696. 

The obligation to fulfil a vow is stronger in the case of an
conditional vow, although it is obligatory to fulfil both types, as stated
above. 

Ibn al-Qayyim said: 

If a person says: “If Allaah delievers me I will give in
charity,” then this is a promise that he has made to Allaah and that he must
fulfil, otherwise he will be included in the group mentioned in the verse
(interpretation of the meaning): 

“So He punished them by
putting hypocrisy into their hearts till the Day whereon they shall meet
Him, because they broke that (covenant with Allaah) which they had promised
to Him and because they used to tell lies”

[al-Tawbah 9:77] 

The promise that a person makes to his Lord is a vow that he
must fulfil. The conditional vow is even more essential to fulfil than a vow
in which a person says, “I will do such and such for Allaah.” 

Breaking it will result in the punishment of hypocrisy in the
heart. 

End quote. 

Secondly: 

The Prophet (peace and blessings of Allaah be upon him)
condemned those who made vows but did not fulfil them. Muslim (2535)
narrated from ‘Imraan ibn Husayn that the Messenger of Allaah (peace
and blessings of Allaah be upon him) said: “The best of you are my
generation, then those who follow them, then those who follow them, then
those who follow them.” ‘Imraan said: I do not know whether the Messenger of
Allaah (peace and blessings of Allaah be upon him) said, “and those who
follow them” two times or three. “Then after them will come people who will
bear witness without being asked to do so, who will betray and not be
trustworthy, who will make vows but not fulfil them, and fatness will appear
among them.”  

Al-Nawawi said: 

This shows that it is obligatory to fulfil vows, and there is
no dispute among the scholars concerning that.  

End quote. 

What is meant by the words of the Prophet (peace and
blessings of Allaah be upon him), “and fatness will appear among them” is
that these people will be negligent towards their religious affairs, and all
they will care about is eating, drinking, relaxing and sleeping. The kind of
fatness that is condemned is that which is acquired, not that which is the
way a person is made. And Allaah knows best. See ‘Awn al-Ma’bood,
commentary on hadeeth no. 4657. 

Thirdly: 

Not fulfilling vows is one of the attributes of the
hypocrites. 

Allaah says (interpretation of the meaning): 

“And of them are some who made a covenant with Allaah
(saying): ‘If He bestowed on us of His Bounty, we will verily, give Sadaqah
(Zakaah and voluntary charity in Allaah’s Cause) and will be certainly among
those who are righteous.’

Then when He gave them
of His Bounty, they became niggardly [refused to pay the Sadaqah (Zakaah or
voluntary charity)], and turned away, averse.

So He punished them by putting hypocrisy into their hearts
till the Day whereon they shall meet Him, because they broke that (covenant
with Allaah) which they had promised to Him and because they used to tell
lies.

Know they not that Allaah knows their secret ideas, and
their Najwa (secret counsels), and that Allaah is the All-Knower of things
unseen”

[al-Tawbah 9:75-78] 

Fourthly: 

With regard to the punishment of one who does not fulfil the
promise he made to Allaah: 

There is the fear that Allaah may punish him by instilling
hypocrisy in his heart, so he will meet Allaah as a hypocrite and will be
one of the losers.

As Allaah says in the verse quoted above (interpretation of
the meaning): 

“So He punished them by
putting hypocrisy into their hearts till the Day whereon they shall meet
Him, because they broke that (covenant with Allaah) which they had promised
to Him and because they used to tell lies”

[al-Tawbah 9:77] 

al-Sa’di said (p. 546): 

This means: among these hypocrites are those who made a
covenant with Allaah and said, “If He bestowed on us of His Bounty”
in this world, granting us a life of ease and plenty, then “we will
verily, give Sadaqah (Zakaah and voluntary charity in Allaah’s Cause) and
will be certainly among those who are righteous” and will uphold the
ties of kinship and support the truth and do good deeds. 

Then “when He gave them of His Bounty”, they did not
keep their promise, rather they “they became niggardly [refused to pay
the Sadaqah (Zakaah or voluntary charity)], and turned away” from
obedience and submission and were “averse” i.e., they had no interest
in doing good. When they did not fulfil the promise that they had made to
Allaah, He punished them by “putting hypocrisy into their hearts”
which will last “till the Day whereon they shall meet Him, because they
broke that (covenant with Allaah) which they had promised to Him and because
they used to tell lies”. 

So let the believers beware of this evil characteristic
whereby a person promises his Lord that if a certain hoped-for thing
happens, he will do such and such, then he does not fulfil that promise, for
Allaah may punish him with hypocrisy just as He punished the people
mentioned here. 

The Prophet (peace and blessings of Allaah be upon him)
said, according to the hadeeth proven in al-Saheehayn: “The signs of
the hypocrite are three: when he speaks, he lies; when he makes a covenant,
he betrays it; and when he makes a promise, he breaks it.” 

This hypocrite who made a promise to Allaah that if Allaah
gave him of His bounty he would give charity and be among the righteous,
spoke and lied, make a covenant and betrayed it, and made a promise and
broke it. Hence those who do such evil actions are addressed with the words
(interpretation of the meaning): 

Know they not that Allaah knows their secret ideas, and
their Najwa (secret counsels), and that Allaah is the All-Knower of things
unseen”

[al-Tawbah 9:78] 

Allaah will recompense them for their deeds which are known
to Him. 

And Allaah knows best.