Jurists differ where the sub-lessee pays more than the original rent. Imam al-Shafi‘i and the preferred Hanbali view allow the sub-lessor to keep the surplus. Imam Abu Hanifah takes a more cautious position and does not allow keeping the surplus in the ordinary case.
Under the Hanafi view discussed here, if the lessee materially improves the property or the sub-lease uses a different currency, a higher rent may be retained.