I was with Abi Abdillah, Ja’far bin Muhammad al-Sadiq (as), and a man from the people of Toos entered – and he said: “Oh son of Rasool-Allah, what is [the reward] for the one who visits the shrine of Abi Abdillah al-Hussain bin Ali (as)?
He [al-Sadiq] replied: “Oh Toosi, whoever visits the shrine of Abi abdillah al-Hussain bin Ali (as), while he knows he is an Imam [appointed] by Allah and obeying him is obligatory upon the servants [of Allah], Allah forgives whatever comes from his sins and what has passed, and intercession is accepted for seventy sins, and Allah (azwj) does not leave anything asked for at the shrine except that he gives it.”
He [the narrator] said: Then Musa bin Ja’far (as) [al-Kadhum] entered, and he [al-Sadiq] sat him [al-Kadhum] on his lap. He kissed him between his eyes, then he turned [towards al-Toosi] and he [al-Sadiq] said to him: “Oh Toosi, verily he [al-Kadhum] is the Imam and the Caliph and the Hujjah after me. From his loins there will come a man who will be pleasing to Allah (azwj) in the heavens and for his servents on earth. He will be oppressively and cruely killed on your plains with poison. He will be buried there as a stranger. Indeed, the one who visits him while he is estranged – while he knows that he is an Imam following his father, where obeying him is obligatory by the order of Allah (azwj), it will be as if he has visited the shrine of Rasool-Allah (sawa).

Sanad: Muhammad bin Ibrahim bin Ishaac al-Taalqaani, from Ahmed bin Muhammad al-Hamdaani the servent of bani Hashem, from al-Mundhir bin Muhammad, from Ja’far bin Sulaymaan, from Abdullah bin al-Fadhil al-Haashimi who said the above hadith.

Source: Amaali al-Sadooq, Page 684; Tahdheeb al-Ahkaam, Volume 6, Page 108

Grading: Sh. Ahmed al-Maahoozi said the chain is Sahih/Authentic and the narrators are reliable [al-Nasoos `ala Ahlul-Khasoos, Page 475-476] (See Image below).