Excerpt from 'Maqtal al-Husayn':
Imam Abu ‘Abdullah, Ja’far as-Sadiq (A), has narrated saying, Al-Husayn (A) visited his brother al-Hasan (A) during his sickness that caused his martyrdom. Having seen his condition, he wept. Al-Hasan (A) asked him, 'O father of ‘Abdullah! What grieves you?' 'I am grieved on account of the harm inflicted on you,' he answered.
Al-Hasan, peace be upon him, said, 'What has been administered to me is only a poison to kill me, but there is no day like your own day, O father of ‘Abdullah, when thirty thousand strong, all claiming to belong to the nation of our grandfather, Muhammad, alleging adherence to the Islamic faith, will assemble to kill you and shed your blood and violate your sanctity and arrest your offspring and women and plunder your wealth.
It is then that Banu Umayyah will be cursed and the sky will rain ashes and blood, and everything, even the beasts in the jungles and the fish in the seas, will mourn you.'