Is it obligatory to return the remaining amount of zakat given to a person to perform the Hajj pilgrimage after its completion?

It is permissible to give a poor person from Zakat funds to perform the obligatory Hajj. If any money remains, he must return it because his taking of Zakat funds is conditioned on need. If he spends it on his need (Hajj), otherwise he must return it. However, if the pilgrim economizes on expenses, accommodation, and transportation, and then some money remains, he is not obligated to return it, because he was given what was sufficient for him, and the surplus was due to his economizing.