The Peak of Eloquence · Hadith 2066 (#Passage #425)

٣٤٨. وَقَالَ (عليه السلام): أَشدُّ الذُّنُوبِ مَا اسْتَهَانَ بِهِ صَاحِبُهُ.

348. Amīr al-mu’minīn, peace be upon him, said: The most serious sin is that which the doer considers light. [1]

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