Kitab al-Tawhid

This book is a hadith collection wherein Muhammad b. 'Ali b. Babiwayh, known as al-Shaykh al-Saduq, with the slightest degree of interference in the texts of narrations, presents a diverse range of theological and philosophical issues surrounding the nature of God, and the relationship with the world.

Rather than write a work of dialectic theology (kalām), al-Ṣadūq relies almost entirely on the transmitted sayings (ḥadīth) of the Prophet and the impeccable Imams of the Twelver (Ithnāʿasharī) tradition that engage directly with questions such as the Oneness of God, free will and predestination, and the significance of revelation.

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