The frame of this prayer niche, from a 14th century theological school in Isfahan, carries a quote from the Quran, verse 9:18-22 reading:
“Said the Prophet (on him be blessing and peace) . . . witness that there is no God save Allah and that Muhammad is his Apostle and the Blessed Imam, and in legal almsgiving, and in the pilgrimage, and in the fast of Ramadan, and he said, on him be blessing and peace.”
And the center panel reads:
“The Prophet (may blessings and peace be upon him) said: The mosque is the abode of every believer.”
Reed Enger, "Mihrab — Prayer Niche," in Obelisk Art History, Published July 22, 2017; last modified May 30, 2020, http://arthistoryproject.com/timeline/middle-ages/medieval-persian-art/mihrab-prayer-niche/.