This is the Koca Mustafa Paşa complex. It's mosque is a former church, St. Andrew in Krisei. Inside are some good capitals, the light was too low to take their picture.Nearby is the shrine of the famous Istanbul folk-saint Sümbül Efendi, who was the first sheik of the dervish tekke which was established here in the 16th century.

Another shrine at the same complex.

On the picture: The ‘Çifte Sultanlar Türbesi’, grave monument of Hatice and Zehra, granddaughters of Hz. Ali
(the cousin and son-in-law of the prophet Muhammad, and caliph from 656 to 661). Tradition tells the girls fled the Muslim territories in 680 AD, following the Battle of Karbala (where nearly all male descendants of Muhammad were killed or murdered) and sought refuge in Constantinople. The Byzantine emperor granted them to stay in the women’s monastery of Ayios Andreas en te Krisei (converted into the Koca Mustafa Paşa Camii around 1490), without having to renounce their Islamic faith. After their death, they were buried in the monastery’s garden.
The mausoleum is also called ‘Peygamber Torunları Türbesi’ (Mausoleum of the Prophet’s grandchildren). Its present form dates from the early 19th century, when Mahmut II had it renewed.

Correspondent: J.M.Criel, Antwerpen.
Sources: Website of ‘mustafacambaz.com’ & Vikipedia/Wikipedia .