Ibn Abbas (may Allah be pleased with them both) said: The Messenger of Allah (peace and blessings be upon him) fasted the day of Ashura and ordered that it be fasted. The Companions said: O Messenger of Allah, it is a day that the Jews and Christians hold in great esteem. The Messenger of Allah (peace and blessings be upon him) said: "Next year, if Allah wills, we will fast the ninth." But before the next year came, the Messenger of Allah (peace and blessings be upon him) passed away.
Hadith Referenceالمعجم الكبير للطبراني / باب العين / 10739