As-Salamu ‘Alaykum. After the death of my mother, I made a vow to give a certain sum as a monthly charity on her behalf. But I failed to fulfill the vow due to debts. Now I feel guilty and have started to fulfill the vow monthly. What about the many years in which I did not fulfill the vow? Until when should I keep on fulfilling the vow?

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 was narrated on the authority of ‘Aa’ishah that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever vowed to obey Allaah, let him do so; and whoever vowed to disobey Him should not do so." [Al-Bukhari]

As you have made a vow to obey Allaah Almighty, you are required to fulfill it. If you are unable to fulfill the vow, then you are required to give an expiation for breaking an oath. It was narrated on the authority of Ibn ‘Abbaas that the Prophet, sallallaahu ‘alayhi wa sallam, said: "Whoever made a vow that he is unable to fulfill, its expiation is the same as that of an oath." [Abu Daawood and Ibn Maajah]

As for the past years when you failed to fulfill the vow, you are required to fulfill it once you become able. But if it is evident that you will never be able to fulfill the vow, you have to give an expiation for each month.

You are required to continue fulfilling the vow according to the intention you had upon making it, whether it was a year, ten years or forever. The wording of the question indicates that you are required to permanently give this sum every month.

Allaah Knows best.