The Ücbaş Camii (“Three Heads’ Mosque”), in the Fatih district (northwestern part of Stambul).
Built in 1532, and restored around 1735, in 1960 and last in 1989. The mosque was commissioned by Ataullah oğlu Nureddin Hamza (Nureddin Efendi), who was born in the village of Ücbaş (near Karasu/Sakarya province) and had served as kadı (judge) in Amasya. Together with his mosque, he had a medrese/school built too, which was in a sorry state, but has been restored in 2012.
Some sources consider this mosque and medrese to be the first buildings that Mimar Sinan erected in Istanbul (before he was promoted to ‘baş mimarı’/imperial chief architect). The attribution of the medrese is certain, that of the mosque probable.

On the picture: the ‘kitabe’ (building inscription) above the door giving access to the mosque’s courtyard.
It gives the date (939 H = 1532/33 AD), the name (‘Üçbaş Camii’) and the commissioner of the mosque.

Correspondent: J.M.Criel, Antwerpen.
Sources: Website of ‘istanbuldakicamiler.com’ & Wikimapia .