The Book of Occultation — al-Ṭūsī · Hadith 757 (#Ḥadīth #6)
Chapter 52 | Some Qualities, practices and manners of the Master of the Age
488- الفضل بن شاذان، عن عثمان بن عيسى، عن صالح بن أبي الاسود، عن أبي عبدالله عليه السلام قال ذكر مسجد السهلة فقال: أما إنه منزل صاحبنا إذا قدم بأهله.
H 488 - It is narrated from Fadhl bin Shazan from Uthman bin Isa from Salih bin Abul Aswad from Imam Ja’far Sadiq that he said when Masjid Sahla was mentioned in his presence: “It will be the residence of our Master of the Affair (Imam Mahdi) when he occupies it with his family.”
Gradings are classical jarḥ-wa-taʿdīl, name-matched to a rijāl index (not individually re-verified).