Some scholars said that vowed prayer and i'tikaf are not to be made up, because they are bodily acts of worship that are not obligatory by virtue of the Sacred Law itself.

Issues:

The first: Is it valid to hire someone to fast on his behalf?

The answer: This is not valid, because it is not valid to hire someone for acts of devotion.

The second: If a person vows to fast the month of Muharram, then dies in Dhu al-Hijjah, it is not made up on his behalf, because he did not live to reach the time when it became due—like one who dies before reaching Ramadan.

The third: If the guardian says, “I will not observe i'tikaf,” or says, “I will not pray,” or says, “I will not perform Hajj,” he is entitled to do so, and there is no substitute for any of these three.

But if he says, “I will not fast,” then one poor person is fed for each day of fasting, provided that the deceased left an estate. By analogy with the madhhab’s principles concerning i'tikaf, someone should be appointed to observe i'tikaf on his behalf, and someone should be appointed to pray on his behalf, since this is an act that must be made up and he left an estate. Thus, according to the principles of the madhhab, payment should be given to one who observes i'tikaf or prays on his behalf; however, I have not seen them explicitly state this.