Marhoom-e-Darbandi (r.a.) reports a tradition from Muntakhab about Imam Sadiq (a.s.) –

‘On sighting the moon of Moharram ul-Haraam, there would be an increase in the grief and sorrow of Imam Sadiq (a.s.).  He (a.s.) used to lament uncontrollably over his grandfather, Imam Husain (a.s.) and people from every region would come to offer their condolences to him (a.s.). They used to recite elegies remembering the calamities upon Imam Husain (a.s.) and beat their chests in grief. When they would conclude their lamentation, Imam (a.s.) would address them saying,

O people! Know that Imam Husain (a.s.) is alive before Allah and is acquiring his sustenance as he desires. His attention is constantly on Karbala where he was martyred along with his companions. He witnesses the visitors to his grave, those who weep upon him and mourn him. He recognises those who grieve over him and knows their names and the names of their fathers. He is cognisant of their position and status in Paradise. Surely, the Imam (a.s.) knows those who lament him and he (a.s.) seeks forgiveness for them. He recommends their forgiveness to his holy grandfather (s.a.w.a), his respected father (a.s.) and mother (s.a.) and his compassionate brother (a.s.).’’

The Imam (a.s.) also said, “If only the visitors to my grave and those who cry out of grief were aware of their reward and status before Allah, they would be pleased with their lamentation. Surely, my visitor and mourner will return to his family while he is happy and content. When he gets up from the gathering of mourners, he will not have a single sin to his name and he will be as when his mother had given birth to him.”

Source: Tradition from the book Asraare Shahaadat by Marhoom-e-Darbandi (r.a.)