The Messenger of Allah ﷺ sent me to my people of Aslam and said, "Instruct your people to fast this day, the day of Ashura. Whoever among them you find has already eaten in the early part of the day, let him fast the remainder of it."
حدثنا يعقوب بن إبراهيم قال حدثنا أبي عن ابن إسحاق قال حدثني عبد الله بن أبي بكر بن محمد عن حبيب بن هند بن أسماء الأسلمي
بعثني رسول الله ﷺ إلى قومي من أسلم فقال مر قومك فليصوموا هذا اليوم يوم عاشوراء فمن وجدته منهم قد أكل في أول يومه فليصم آخره
Its isnad is sahih. The hadith scholars graded it sahih, though there is some inconsistency in its chain. Abdullah bin Abu Bakr bin Muhammad bin Amr bin Hazm Ansari, the judge, is a well-known trustworthy narrator, and his hadith appears in the major hadith collections. Habib bin Hind bin Asma bin Hind was deemed trustworthy by Ibn Hibban, while Bukhari and Abu Hatim made no comment on him.Hakim graded the hadith sahih in 3/529, and Dhahabi agreed with him. Haythami said in 3/185, "The narrators of Ahmad are trustworthy."This hadith was mentioned previously in similar wording at 15416.