I have heard of cases whereby when an adult passed away without performing the Hajj, his Hajj is performed on his behalf (either voluntarily or sponsored) by a living person. Under what condition(s) does performing Hajj for such a dead person become obligatory?

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 is His slave and Messenger.

We have already clarified in Fatwa 87129 the conditions when a Muslim is obliged to perform Hajj. A person who died after having fulfilled these conditions and yet did not perform Hajj, it is an obligation to perform Hajj on behalf of such a person from his inheritance whether or not he made a will to this effect [for Hajj]. This is the preponderant opinion in our view (in Islamweb) and it is the view of the Hanbali and Shaafi'ee Schools of jurisprudence. Also, his debts must also be paid from his inheritance whether or not he made a will about it.

If he has no inheritance from which one can perform the obligatory Hajj on his behalf, then it is desirable for someone to perform Hajj on his behalf (from their own money). However, it is a condition on whoever wants to perform Hajj on his behalf to have performed his own obligatory Hajj, as clarified in Fatwa 84509.

Finally, it should be noted that some jurists conditioned that the one performing Hajj on behalf of the deceased must originate from his country because he was obliged to perform Hajj from his own country, and therefore, it is an obligation for a person who wants to perform Hajj on his behalf to do that from his country [country of the deceased]; this is the view of the Hanbali School of jurisprudence. However, if this is not facilitated, then it is permissible to do so from any other country or place.

Allaah Knows best.