The Book of Occultation — al-Ṭūsī · Hadith 491 (#Ḥadīth #1)

لا علة تمنع من ظهوره إلا خوفه على نفسه من القتل، لانه لو كان غير ذلك لما ساغ له الاستتار، وكان يتحمل المشاق والاذى، فإن منازل الائمة وكذلك الانبياء عليهم السلام إنما تعظم لتحملهم المشاق العظيمة في ذات الله تعالى.

There is no reason for delay in his reappearance, except danger to his life, which is an obstacle in his reappearance. Its proof is that if there had been some other cause, his remaining in occultation would not have been correct and it is because of this that His Eminence had to bear different kinds of problems and hardships. That is why the ranks and levels of recognition of the Imams of guidance and the divine prophets are very great and lofty; due to which they bear even the great difficulties and hardships for the sake of Almighty Allah.

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