The azan resounds from the Hagia Sophia Grand Mosque, calling Muslim worshippers to prayer.
The former Istanbul museum will hold Muslim prayers for the first time since it was reconverted into a mosque by a presidential decree on July 10.
President Recep Tayyip Erdoğan, who will attend the afternoon prayers, visited the monument on Thursday with his wife Emine for a final inspection.
A green sign with gold lettering in Turkish, Arabic and English was unveiled, which says: The Hagia Sophia Grand Mosque.
