Musnad Ahmad 30:1595

Abu Ja'far narrated to us, 'Abd al-Samad ibn Habib al-Azdi informed us, from his father Habib ibn 'Abd Allah, from Shubayl, from Abu Hurayrah, who said: The Prophet, peace and blessings of Allah be upon him, was fasting on the day of 'Ashura'. He said to his companions: "Whoever among you woke up fasting, let him complete his fast, and whoever has eaten from his family's lunch, let him complete the rest of his day."