The inscriptions on the mihrab and frieze are from the Koran. On the frieze are written the first 30 verses from the Chapter of the Dawn (89). The inscription on the mihrab is from the Chapter of Light (24: 35-36) and translates:
God is the light of the Heavens and the Earth.
His Light is like a niche in which is a lamp---the
lamp enclosed in glass---the glass, as it were, a glistening star. From a blessed tree it is lighted,
the olive neither of the East nor of the West,
whose oil would well neigh shine out, even though fire touched it not! It is light upon light.
God guideth whom He will to His light, and God
setteth forth parables to men, for God knoweth.