The Book of Occultation — al-Ṭūsī · Hadith 766 (#Ḥadīth #15)
Chapter 52 | Some Qualities, practices and manners of the Master of the Age
497- عنه، عن عبدالله بن القاسم الحضرمي، عن عبدالكريم بن عمرو الخثعمي قال: قلت لابي عبدالله عليه السلام: كم يملك القائم؟ قال: سبع سنين يكون سبعين سنة من سنيكم هذه.
H 497 - It is narrated from Fadhl from Abdullah bin Qasim Hadhrami from Abdul Karim bin Amr Khathami that he said: “I asked Imam Ja’far Sadiq about the duration of the rule of Imam Qaim . He replied: He will rule for seven years, but these seven years will be equal to seventy years of your reckoning.”
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).