The hall of the mosque is rectangular in plan and extended along the east-west axis. Four major mosque buttresses divide the hall into separate segments covered by domes. The wall panels and the mihrab (a prayer niche showing the direction to Mecca) are faced with six-sided mosaic tiles and magnificently performed mosaic compositions. Inscriptions have remained around the mihrab niche.
In the south-eastern corner of the mosque there is a roofed passage leading to the grave of Qusam ibn ‘Abbas. It is believed to be the remains of the most ancient part of this group of buildings. An ancient link beam with a carved inscription on one of its surfaces has survived here. Judging by its paleography, this inscription dates from the 11th century.
According to experts, the mosaic decoration of the mihrab niche was made by masters of the Bukhara school. There are two strips with inscriptions in the rectangular cartouche above the mihrab niche. The lower strip (in the thuluth script) contains a fragment from the Koran. The upper inscription (the kufic script) is a formula glorifying Allah:
سبحان الله و بحمده سبحان الله العظيم – «Praise unto Allah by His Glorification! Praise unto Allah, the Most Great!»
Allah, the Almighty said: «And the mosques are for Allah [Alone], so invoke not anyone along with!»
A fragment from the Koran is also cited in the same script along the mihrab niche perimeter.
Allah, the Almighty – praise be unto Him! – said in His clear Book [the Koran]: «Verily! We have seen the turning of your [Muhammad's] face towards the heaven. Surely, We shall turn you to a Qiblah3 that shall please you, so turn your face in the direction of Al-Masjid- al-Harâm [at Makkah]. And wheresoever you people are, turn your faces [in prayer] in that direction. Certainly, the people who were given the Scriptures [i.e. Jews and the Christians] know well that, that (your turning towards the direction of the Ka'bah at Makkah in prayers) is the truth from their Lord. And Allah is not unaware of what they do». Right is Allah, the All-Powerful. His great Messenger [Muhammad] confirmed this. We also witness it, O Lord of the worlds!
A fragment from the Koran written with yellow letters on the green background is repeated two times in the lower part of the mihrab niche.
Whatsoever is on it [the earth] will perish.
You can read more about the inscriptions on the buildings of the memorial ensemble in the book-album “Samarkand. Shakhi-Zinda” series “Architectural epigraphy of Uzbekistan”.