Imam Jafar Sadiq (a.s.), O Dawood! Curse the killers of Imam Husain (a.s.). There is not a servant that after drinking water remembers Imam Husain (a.s.) and curses his killers, but that Allah will write in his deeds one lakh good deeds, will forgive one lakh sins and raise his position by one lakh grades. (Perhaps it is freeing one lakh people from sins). On the Day of Judgment, Allah will make his heart contented and satisfied.
Kaamiluz Ziyaraat, Chapter 34, Tradition No. 1, Pg. 346