I saw the Prophet ﷺ in a dream at midday, standing disheveled and dust-covered, with a flask in his hand containing blood.I said, "May my father and mother be ransom for you, Messenger of Allah, what is this?"He replied, "This is the blood of Husayn and his companions. I have been gathering it all day."We took note of that day, and it was found that he had been killed on that very day.
حدثنا عفان حدثنا حماد هو ابن سلمة أخبرنا عمار
رأيت النبي ﷺ فيما يرى النائم بنصف النهار وهو قائم أشعث أغبر بيده قارورة فيها دم فقلت بأبي أنت وأمي يا رسول الله ما هذا قال هذا دم الحسين وأصحابه لم أزل ألتقطه منذ اليوم فأحصينا ذلك اليوم فوجدوه قتل في ذلك اليوم
Its isnad is sahih. It is a repetition of 2165. The one who says "so we counted, etc." is Ammar bin Abu Ammar, as was made clear there.