A Turkish court ruled in 2020 that Mehmed II's endowment deed still bound Hagia Sophia as a mosque, while an Armenian foundation could not recover its confiscated Istanbul inn

Hagia Sophia was built as a church in the sixth century. After the Ottoman conquest in 1453 it became a mosque. A few years later Sultan Mehmed II made it part of his waqf, a perpetual religious endowment. The original endowment charter is lost; a copy made in 1490 lists his Istanbul endowments. A 1934 Cabinet decree turned the building into a museum. On 31 August 2016 an association, which the Harvard Law Review describes as the legal personality of an elderly former teacher, petitioned to reopen it for worship. The Prime Ministry refused on 19 October 2016, and the association appealed to the Council of State. On 10 July 2020 the court's Tenth Chamber annulled the 1934 decree. It held that Mehmed's deed allocated the building as a mosque, that the deed has the force of law, and that the endowed purpose could not be changed by an administrative act. President Erdoğan signed a decree the same day handing the building to the Religious Affairs Directorate. UNESCO said Turkey had not consulted it. Lawyers asked whether the same reasoning would apply to Sanasaryan Han, an inn near Gülhane Park endowed in 1901 by Mıgırdiç Sanasaryan for poor Armenian children, with the Armenian Patriarch as sole trustee. The newspaper Agos reports that the state took it in 1928. The Patriarchate sued and lost, and the state rented the inn out for 20 years while its appeal was pending. Hagia Sophia operates as a mosque; tourists enter free outside prayer times.