Atik Mustafa Pasha Mosque (Turkish: Atik Mustafa Paşa Camii; also named Hazreti Cabir Camii) is a former Eastern Orthodox church in Istanbul, converted into a mosque by the Ottomans. The dedication of the church is obscure. For a long time it has been identified with the church of Saints Peter and Mark, but without any proof. Now it seems more probable that the church is to be identified with Saint Thekla of the Palace of Blachernae (Greek: Άγία Θέκλα τοῦ Παλατίου τῶν Βλαχερνών, Hagia Thekla tou Palatiou tōn Vlakhernōn).