Hadith 4:501
Ibn ‘Ulayyah narrated to us, from Ayyub, from Muhammad, that the Prophet, may Allah bless him and grant him peace, commanded a man from Aslam on the day of ‘Ashura. He said: "Go to your people and command them to fast this day." He said: "I do not see that I will reach them until they have eaten in the morning." He said: "Whoever among them has eaten in the morning, let him fast the remainder of his day, and whoever among them has not eaten in the morning, let him fast."
حدثنا بن علية عن أيوب عن محمد أن النبي صلى الله عليه وسلم أمر رجلا من أسلم يوم عاشوراء فقال إئت قومك فمرهم أن يصوموا هذا اليوم فقال ما أراني آتيهم حتى يصطبحوا فقال من اصطبح منهم أن يصومه بقية يومه ومن لم يصطبح منهم أن يصوم