The first extant investiture letter for a ṣāḥib al-shurṭa can be found in a compendium of the rasāʼil (government letters) written by the head of the Buyid chancery in Baghdad, Abū Isḥāq Ibrāhīm al-Ṣābiʾ (d. 384/994). This letter was written for an official appointed as the ṣāḥib al-shurṭa over the city of Wāsiṭ in Iraq during the reign of the Buyid amir of Iraq, ʿIzz al- Dawla (r. 356-367/967-978). The text gives rare insight not only into the investiture genre for the shurṭa, but also into how his duties were shaped by sectarian conflicts raging in Iraq.
This invesiture letter along with other rasāʼil were edited by Iḥsān Dhūnūn al-Thāmirī in Diwān Rasāʾil al-Ṣābiʾ: the Registry of al-Ṣābiʾ Letters. London: Al-Furqān Islamic Heritage Foundation, 2017. A scan of this investiture letter from Volume 1 has been made available.