What is the function of duʿa in Imami Shiʿi intellectual and spiritual life? How does it correspond to other dimensions of Imami religiosity, e.g., the legal (fiqhi), theological (kalāmi), and literary (adab) discourses? This paper will explore these questions through a close reading of the famous compilation of Shaykh al-Ṭāʾifah al-Ṭūsī (d. 1067), Misbāḥ al-Mutahajjid. The Miṣbāḥ presents duʿa (supplication) as an extension of a Muslim’s legal obligation, first enumerating the various mandatory acts and their conditions throughout the Islamic calendar, e.g., the canonical prayer or the Ramadan fast, then presenting duʿas in terms of those obligations. Hence, this text neither fits the genre of the legal nor the prayer manual, rather unites the two in a continuum of praxis. This also hints at the internal logic at work in a prayer manual: the author presents abridged chains of transmitters to give a sense of authenticity, but does not fixate on proper chains; he provides different recensions of a single duʿa; and he includes ziyārāt (pilgrimage) formulas alongside duʿas. This evinces a particular internal logic to the Miṣbāḥ, and raises a number of questions: According to al-Ṭūsī, does a prayer have to be authentic? Why? And what are the requirements to attain authenticity? These lead us to a more fundamental question: what place did duʿa have viz-a-viz theology, particularly with respect to al-Ṭūsī’s theological position as a member of the more rationalist school of Imami kalām? Indeed, on one later reworking, the Minhāj al-Ṣalāḥ of “Allamah” Ibn Muṭahhar al-Ḥillī (d. 1325), the Miṣbāḥ becomes a launching point for a theological discourse according to Imami creed. How does this prayer manual help us understand a different side to Imami theology as expressed by al-Ṭūsī and al-Ḥillī, a theology that could not be expressed in terms of the genre of discursive theology (kalām)?