ashura

Reported by Muslim
The Prophet said:"If I survive till next year, I will definitely observe fast on the 9th of Muharram [as well].”

Sahih Bukhari Hadeeth. Vol.3 Book :31. Fasting. No.117.
Narrated 'Aisha:
(The tribe of) Quraish used to fast on the day of Ashura' in the Pre-lslamic period, and then Allah 's Apostle ordered (Muslims) to fast on it till the fasting in the month of Ramadan was prescribed; whereupon the Prophet said, "He who wants to fast (on 'Ashura') may fast, and he who does not want to fast may not fast."

Sahih Bukhari Hadeeth. Vol.3 Book :31. Fasting. No.220.
Narrated Aisha:
Quraish used to fast on the day of 'Ashura' in the Pre-lslamic period, and Allah 's Apostle too, used to fast on that day. When he came to Medina, he fasted on that day and ordered others to fast, too. Later when the fasting of the month of Ramadan was prescribed, he gave up fasting on the day of 'Ashura' and it became optional for one to fast on it or not.

Sahih Bukhari Hadeeth. Vol.3 Book :31. Fasting. No.222.
Narrated Ibn 'Abbas:
The Prophet came to Medina and saw the Jews fasting on the day of Ashura. He asked them about that. They replied, "This is a good day, the day on which Allah rescued Bani Israel from their enemy. So, Moses fasted this day." The Prophet said, "We have more claim over Moses than you." So, the Prophet fasted on that day and ordered (the Muslims) to fast (on that day).

Sahih Bukhari Hadeeth. Vol.3 Book :31. Fasting. No.224.
Narrated Ibn 'Abbas:
I never saw the Prophet seeking to fast on a day more (preferable to him) than this day, the day of 'Ashura', or this month, i.e. the month of Ramadan.