Kitāb al-Tawḥīd (Arabic: کتاب التوحید ) (lit. The Book of Divine Unity) is one of the earliest and the most significant theological sources which is compiled by the reputable Muhaddith (hadith scholar) of fourth/tenth century, Muhammad b. 'Ali b. Babiwayh, known as al-Shaykh al-Saduq. This book is about monotheism in its general sense (knowing about Allah) and comprises narrations about the unity of the Divine essence, affirmation and negation attitudes in understanding Divine attributes, attributes of essence and attributes of action and their relation to the Divine essence, eternity and temporality, predestination and divine providence, determinism and absolute freewill and the related topics.This book is a hadith collection wherein al-Shaykh al-Saduq, with the slightest degree of interference in the texts of narrations, presents theological discussions. His motive for compiling such a book was to respond to the accusations which were made against Shi'a beliefs by the enemies of Shi'a. This book has always been at the center of Shi'a scholar's attention as one of the most authentic hadith sources whose content would be cited for various theological discussions.