Musnad Ahmad 25:327

'Abd al-Rahman narrated to us, Hammad ibn Salamah narrated to us, from 'Ammar ibn Abi 'Ammar, from Ibn 'Abbas, who said: "I saw the Prophet, peace and blessings of Allah be upon him, in a dream at midday, disheveled and covered in dust, with a vial in his hand containing blood, which he was collecting or tracking something within it. I said: 'O Messenger of Allah, what is this?' He said: 'The blood of al-Husayn and his companions; I have not ceased tracking it since today.'" 'Ammar said: "So we noted that day, and we found that he was killed on that day."