The chamber has a large arched window looking back into the prayer hall.[1] According to Xavier Salmon, the chamber was originally a bayt al-'itikaf (Arabic: بيت الاعتكف‎), a room for spiritual retreat; a feature which became more common in later Saadian mosques in Marrakesh (e.g. the Mouassine Mosque and Bab Doukkala Mosque). In later centuries it was converted into a library, probably on the initiative of Moulay Rashid (in the late 17th century), who may have also redecorated parts of the mosque at the same time.[2]