The Book of Occultation — al-Ṭūsī · Hadith 389 (#Ḥadīth #38)

قال: قوله تمسكوا بالأول حتى يظهر لكم الآخر هو دليل على إيجاب الخلف، لأنه يقتضي وجوب التمسك بالأول ولا يبحث عن أحوال الآخر إذا كان مستورا غائبا في تقية حتى يأذن الله في ظهوره ويكون الذي يظهر أمره ويشهر نفسه على أن القائلين بذلك قد انقرضوا، والحمد لله.

It is unreasonable, as this is a singularly narrated tradition. Besides, Saad Ibn Abdullah has interpreted it thus, “Adhere to the first one until the second one appears to you.” In this case, it is a proof of the successor , because it requires to adhere to the first and not to seek the news of the next when he is in hiding and occultation due to dissimulation (Taqayyah), until Allah gives him permission to appear and he will be the one whose rule will be manifested and whose person will be famed. Furthermore, believers in this dogma no longer exist, and praise belongs to the Lord.

Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).