The inscription is from the Qu'ran, sura al-rum (xxxvi), parts of v.12.
Other tiles in this series, all of which are noted by Carboni as having inscriptions from the same sura of the Qur'an, are in various museum collections including the Metropolitan Museum of Art, the Victoria and Albert Museum in London, the Österreichischen Museum für Angewandte Kunst in Vienna, and the Museo Nazionale del Bargello in Florence (Carboni, Stefano and Masuya, Tomoko: Persian Tiles, New York, 1993, no.22, p.27). Two further examples were sold in these Rooms 12 October 1999, lot 299 and 11 Ocober 2000, lot 233. The Bargello tile has been published since the New York catalogue as being inscribed with Qur'an sura v, v.55 (Islam, Specchio d'Oriente, exhibition catalogue, Florence, 2002, no.130, p.162).
Sheila Blair has suggested that this series was originally made for the South Wall of the Tomb of 'Abd al-Samad in Natanz (Blair, S.S.: The Ilkhanid Shrine Complex at Natanz, Cambridge, Mass. 1985, p.64).