Probably the back of the Sultan Mehmet V Reşat Türbesi, the front is more ostentatious. I am not certain, though, finding only some pictures on Google maps. About this building the Strolling Through Istanbul guidebook states he died in 1918, was the last sultan to be buried in his own country, and the only one to be buried in the holy precincts of Eyüp.
One of several pictures I took during a visit in the early evening in May 2014. Many spots were much quieter than during the daytime, the mosque itself was still rather busy.
In this case with Eyüp I mean the area, rather than the mosque alone.