Hirami Ahmet Pasha Mosque also known as Saint John the Forerunner by-the-Dome (Ἃγιος Ἰωάννης ὁ Πρόδρομος ἐν τῷ Τρούλλῳ, Hagios Ioannis ho Prodromos en tō Trullō). Strolling through Istanbul saw it in a sorry state: a nursery for stray pupuppies. In the meantime things have changed, when I visited it was a striving Koran school. This implied we (me and Raffaele d’Amato, a specialist in things Byzantine) could not take all pictures we wanted to take.
There are some obvious traces of Byzantine building, though Strolling indicates the four original columns supporting the dome were purloined, to be replaced by poorer ones, with awkward capitals. Also the restored brickwork was wrong.
The Wikipedia has: “Nothing is known about this church before the conquest of Constantinople in 1453. The appellation "troullos" (Latin trullus, Italian trullo, dome) probably comes from a dome-roofed palace that used to be in the neighborhood. The style of construction dates the building to the 12th century.
When the Patriarchate was moved from the Church of the Holy Apostles to that of Pammakaristos between 1454 and 1456, Patriarch Gennadios displaced some nuns who were living in the monastery of Pammacharistos to the small nunnery of Troullos, which was probably founded on this occasion. At the end of 16th century, during the reign of Sultan Murat III, Hırami Amet Pasha, formerly Agha of the Jannissaries, converted the church of the Pammakaristos into a mosque. He did the same with the church of Saint John, closing the nunnery and expelling the nuns. This should have occurred between 1587 or 1588 (the years of the conversion of Pammakaristos) and 1598, the year of his death. The small building had gone to ruin by the beginning of the 20th century. It was carefully restored and reopened to Islamic worship in 1961.“

I have no pictures of the inside: it was Ramadan, and a rather large group of believers was gathered in the small space, the Koran was being recited. It was not sensible to play the tourist.