Ertuğrul Tekke Mosque is a historic mosque located in Beşiktaş district, Istanbul, Turkey. It was built by Ottoman sultan Abdul Hamid II in 1887 and considered an example of the mosques of the late Ottoman era. It was built in the form of an integrated complex that includes a tekke, a guest house, a türbe (Tomb), and a library, in addition to the mosque. The mosque is dedicated to the Libyan Sufi, Sheikh Hamza Zafir, the founder of the Medeni branch of Shadhili tariqa, and it is named after Ertuğrul Gazi who was a 13th-century bey and the father the founder of the Ottoman Empire, Osman I.