Question
I have made vow last month and it was about quitting smoking. The vow was to keep away from smoking and if I break I will fast one whole month. I broke the vow. So, I am suppose to fast now or there are some other ways that I can fulfil my fast like feeding needy people. Please let me know so I know what to do upon receiving your answer.
Fatwa
All perfect praise be to Allah, The Lord of the Worlds. I testify that there is none worthy of worship except Allah, and that Muhammad is His slave and Messenger.
If the situation is as you mentioned in the question that you made a vow to fast a whole month if you return to smoking, then you have the choice either to fulfil your vow or to expiate for your oath. However, it is better to fulfil your vow in order to avoid the difference of opinion on this issue.
To explain this, if a man says: 'If I ever do such and such a matter [that he is determined not to do], then I would offer to Allah such and such, (an act of obedience to Allah)', then this is called the vow of obstinacy and anger.
Indeed the scholars differed in opinion whether a person is obliged to fulfil the very vow he made [as he failed to fulfil it], or does he have the choice either to fulfil the vow or expiate for it, or he is only obliged to expiate for it. So some scholars are of the view that he has to choose either to fulfil his vow or to expiate for breaking his oath, which is the view of the Hanbali school, An-Nawawi from the Shaafi'ee school, and the opinion of Muhammad Ibn Al-Hassan from the Hanafi school.
However, other scholars are of the view that he is obliged to fulfil the vow like the Maaliki school; yet others are of the opinion that he is only obliged to expiate for breaking his oath.
To conclude, there is no doubt that in order to be on the safe side, it is better for you to fast for a whole month as a fulfilment to your vow so that you would avoid the difference of opinion on the issue. Nonetheless, you may also act according to the opinion that you are only obliged to expiate for your oath.
Allah Knows best.