Musnad Ahmad 2540

It was narrated that Ibn ‘Abbas (رضي الله عنه) said: I saw the Prophet (ﷺ) in a dream when I slept in the middle of the day. He was standing, looking dishevelled and dusty, with a bottle in his hand in which there was blood. I said: May my father and mother be sacrificed for you, O Messenger of Allah. What is this? He said: This is the blood of al-Husain and his companions. I have been collecting it all day. We worked out that day, and we found that it was the day on which he was killed.