The Book of Occultation — al-Ṭūsī · Hadith 180 (#Ḥadīth #1)
Chapter 18 | What is the difference between a hidden Imam and an Imam who does not exist or one that exists in the heavens?
وقد بينا فيما تقدم الفرق بين وجوده غائبا لا يصل إليه أحد أو أكثرهم وبين عدمه حتى إذا كان المعلوم التمكن بالأمر يوجده.
We have also previously elucidated the difference between the instance that he exists in hiding where no one or few can reach him and the instance of his non-existence until his capacity of governance is known and then God creates him.
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).