Fasting on the day of Arafah & Others

Hunaydah ibn Khaalid narrated upon the authority of his wife who said, "Some of the wives of the Prophet (salallaahu 'alaihiwasallam) told me that the Prophet (salallaahu 'alaihiwasallam) used to fast the Day of 'Aashoorah, the first nine days of Dhul-Hijjah, and three days out of every month*." 

(Imam Ahmad, An-Nasaaee; Imam Al-Albanee declared it Saheeh)