Musnad Abu Ya'la al-Mawsili 243:112

Ishaq narrated to us, Abu Usamah narrated to us, he said: Abu Umays ibn Abdullah ibn Abd al-Rahman ibn Abdullah ibn Mas'ud narrated to me, from Qays ibn Muslim al-Jadali, from Tariq ibn Shihab, from Abu Musa, who said: The day of Ashura was a day that the Jews would fast and venerate. When the Messenger of Allah (peace be upon him) arrived in Medina, he commanded that it be fasted.