Mukhtasar Bukhari

Umm al-Mu'minin Aisha Siddiqa (may Allah be pleased with her) says: (We) used to fast on the day of Ashura before the fasting of Ramadan was made obligatory, and it was a day on which the covering was placed over the Ka'bah. Then, when Allah Almighty made Ramadan obligatory, the Messenger of Allah (peace and blessings of Allah be upon him) said: "(Now) whoever wishes to fast on Ashura may do so, and whoever does not wish to fast may leave it."

Narrated by Sayyiduna Abu Sa'id Khudri (may Allah be pleased with him) from the Noble Prophet (peace and blessings of Allah be upon him) that he (peace be upon him) said: "Even after the emergence of Gog and Magog, Hajj and 'Umrah of the Ka'bah will be performed."