Kitāb al-tawḥīd is work that is attributed to Abū Manṣūr Muḥammad b. Muḥammad al-Mātuīdī (d. 333/994) the eponym of the theological school. It was published in 3 Arabic editions all based on this manuscript, one in Beirut 1970, edited by Fathalla Kholeif and the other two in Istanbul (2001 and 2003, repr. 2019) edited by Bekir Topaloǧlu and Muhammed Aruçı. For more information see Mustafa Cerić’s Roots of Synthetic Theology in Islām: A Study of the Theology of Abū Manṣūr al-Māturīdī (d. 333/944) Kuala Lumpur, ISTAC 1995. pp. 49–61.
Cambridge University Library holds Kitāb al-tawḥīd (MS Add.3651) which contains the only extant copy of al-Māturīdī’s Kitāb al-tawḥīd. This treatise discusses the opinions of different religious groups -both Muslim and non-Muslim- on a variety of theological issues, with especial attention to the polemics concerning the attributes of God.
The original Manuscript is found here: https://cudl.lib.cam.ac.uk/view/MS-ADD-03651/1
In one PDF file is found here: https://archive.org/details/msadd3651