Hadith 4:490
Abdullah ibn Numayr narrated to us, he said: Ubaydullah ibn Umar narrated to us, from Nafi’, from Ibn Umar, that the people of the Jahiliyyah used to fast the day of Ashura, and that the Messenger of Allah (peace and blessings of Allah be upon him) fasted it, and the Muslims [fasted it] before Ramadan was made obligatory. When Ramadan was made obligatory, the Messenger of Allah (peace and blessings of Allah be upon him) said: "Ashura is a day from the days of Allah, so whoever wishes may fast it, and whoever wishes may leave it."
حدثنا عبد الله بن نمير قال حدثنا عبيد الله بن عمر عن نافع عن بن عمر أن أهل الجاهلية كانوا يصومون يوم عاشوراء وأن رسول الله صلى الله عليه وسلم صامه والمسلمون قبل أن يفترض رمضان فلما افترض رمضان قال رسول الله صلى الله عليه ( ( ( عاشوراؤ ) ) ) وسلم عاشوراء يوم من أيام الله فمن شاء صامه ومن شاء تركه