The scholars’ preponderant opinion on this issue is that it is not obligatory to make up for the voluntary I‘tikaaf (seclusion in the mosque), whether there is an excuse for interrupting it or not. However, it is favorable to make up for the voluntary I‘tikaaf because the Prophet, , did that when he interrupted his I‘tikaaf. He made up for it in the month of Shawwaal. This is the opinion adopted by Shaykh Al-Islam and the majority of scholars.
On the other hand, the obligatory I‘tikaaf must be compensated for as one will not be free yet from liability if his I‘tikaaf was vowed and was interrupted. In this case, he will be required to repeat his I‘tikaaf. There is an extremely fine issue that arises here: whoever vows to make I‘tikaaf ten consecutive days, then makes I‘tikaaf only for five days, should he repeat the whole ten days? In other words, he observes I‘tikaaf for five days and then invalidates his I‘tikaaf by going out of the place of I‘tikaaf: should he make up for ten or five days?
In this case, if one interrupts his I‘tikaaf with a Sharee‘ah-approved excuse, the five days he spends in I‘tikaaf will be counted and whenever his excuse is over, he must return and complete his I‘tikaaf. Nonetheless, if one invalidates his I‘tikaaf for an excuse that is not approved by the Sharee‘ah, then he would have to repeat the whole ten days. In case one vows to make I‘tikaaf for ten days without making mention of their being consecutive or not, then every day he spends in I‘tikaaf will count and he will have only to make I‘tikaaf for the remaining days. However, he will have to make up for the day on which he went out because he did not complete it.
One final question here: should the heir make up for the I‘tikaaf due on the one he inherits from?
If one’s father dies without fulfilling a vow, should he fulfill it on his behalf?
The majority of scholars are of the opinion that he does not have to fulfill it on his behalf because there is no evidence supporting this. Imaam Ahmad said that the heir should fulfill on the deceased’s behalf if the vow was one that is favorable to fulfill, however, it is not obligatory because of the Hadeeth: “Whoever dies while having fast to be compensated, his heir should fast on his behalf.” He said that I‘tikaaf is more like the fast than the prayer. This is a reasonable opinion. If one does not make this, he may still feed a needy person for every day or, as some scholars mentioned, he has to pay an oath-expiation because the expiation of the vow is like that of the oath as mentioned in authentic Hadeeths.