Observing Saum (fast) on the day of Ashura (tenth of Muharram).
Narrated Aisha (RAa): Quraish used to fast on the day of Ashura in the Pre-Islamic Ignorance Period, and Allah's Messenger (SAW) too, used to observe Saum (fast) on that day. When he came to Al-Madina, he observed Saum (fast) on that day and ordered others to observe Saum (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 observe Saum (fast) on it or to leave its Saum (fast).
