can you say that vowed i'tikaf and prayer may be performed on behalf of the one who made the vow?

We reply: The Prophet, peace and blessings be upon him, drew an analogy between acts of worship and ordinary matters, saying: “Consider: if your mother owed a debt …” This vowed i'tikaf, for example, has become a debt owed by the person who made the vow; indeed, it is more akin to vowed Hajj than to an ordinary debt.

Accordingly:

• Hajj is performed on behalf of the deceased, whether it was an original obligatory duty or a vow, without any difference of opinion.

• Fasting is made up if it was vowed. If it was obligatory by virtue of the Sacred Law itself, there is a difference of opinion; but the stronger view is that it should be made up. If the guardian does not make it up, and the deceased left an estate, then a poor person must be fed on his behalf for each day of fasting.

• Prayer is not made up, without any difference of opinion, if it was obligatory by virtue of the Sacred Law itself. If it was obligatory through a vow, then it is made up according to the madhhab.

I'tikaf cannot be obligatory by virtue of the Sacred Law itself; rather, it becomes obligatory only through a vow, in which case his guardian observes i'tikaf on his behalf.

Those who hold that vowed prayer and i'tikaf may be made up cited the Prophet’s words: “Consider: if your mother owed a debt, would you pay it off?” She replied, “Yes.” He then said, “Fulfil what is due to Allah.” (1) Thus, the Prophet made a vow a debt; and since a vow is a debt, and the Prophet drew an analogy between the debt owed to Allah and a debt owed to another person, we say: there is no difference between the debt of prayer and the debt of fasting.