On the picture: A broad calligraphic border of Iznik tiles (with its script in white, on a blue base), running around three quarters of the prayer hall. The text consists of a ‘Besmele/Bismillah’ (the phrase recited before each ‘sura’/chapter of the Kuran) and two suras (the 94th and the 122th). It is the work of Hattat (= calligrapher) Çerkez Hasan. Classical Ottoman, about 1573.

Correspondent: J.M.Criel, Antwerpen.
Sources: ‘Türkiye Tarihi Yerler Kılavuzu’ – M.Orhan Bayrak, Inkılâp Kitabevi, Istanbul, 1994 & Wikipedia.