The Book of Occultation — al-Ṭūsī · Hadith 659 (#Ḥadīth #1)

قد بينا بالاخبار الصحيحة بأن مولد صاحب الزمان عليه السلام كان في سنة ست وخمسين ومائتين وأن أباه عليه السلام مات في سنة ستين فكانت له حينئذ أربع سنين فيكون عمره إلى حين خروجه ما يقتضيه الحساب ولا ينافي ذلك الاخبار التي رويت في مقدار سنه مختلفة الالفاظ.

We have previously, through authentic reports, narrated that the holy birth of Imam Mahdi occurred in 256 A.H. and his holy father passed away in 260 A.H. Thus the Imam was four years old at that time. However, the age of the Imam till the time of his reappearance and advent is a number, which requires calculation with the reports that are recorded about the age of the Imam at the time of reappearance [like reports, which say that he would appear like a man of forty] are differently worded, have no contradiction with reports, which will be mentioned in this section.

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