The Book of Occultation — al-Ṭūsī · Hadith 755 (#Ḥadīth #4)
Chapter 52 | Some Qualities, practices and manners of the Master of the Age
486- الفضل بن شاذان، عن إسماعيل بن عياش، عن الاعمش، عن أبي وائل، عن حذيفة بن اليمان، قال: سمعت رسول الله صلى الله عليه وآله وسلم يقول وذكر المهدي: إنه يبايع بين الركن والمقام إسمه أحمد وعبدالله والمهدي فهذه أسماؤه ثلاثتها.
486- It is narrated from Fadhl from Ismail bin Ayyash from Amash from Abu Wael from Huzaifah that he said: I heard the Messenger of Allah (s) say when Imam Mahdi was mentioned in his presence: “Indeed his allegiance will be given between Rukn and Maqam. He has three names: Ahmad, Abdullah and Mahdi.”
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).