It has been narrated from Hasan ibn Rashid from Abi ’Abdillah [Imam Ja’far ibn Muhammad as-Sadiq] "peace be upon him" that he said, “May I be sacrificed for you! Do the Muslims have a festivity other than the two ’Eid celebrations?” The Imam "peace be upon him" replied, “Yes O’ Hasan! (There is one) greater than these two and much worthier than them.”
The companion replied, “And what day is that?” The Imam said, “The day upon which Amirul Mo’minin [’Ali ibn Abi Talib] "peace be upon him" was appointed as the flag (of guidance) for the people.” The companion then asked, “May I be sacrificed for you! And what should we do (on this day)?” The Imam replied, “You should fast on it, O’ Hasan, and recite many prayers upon Muhammad and his family and disavow yourself towards Allah from all of those who oppressed them;
Surely the Prophets (of the past) also commanded their successors to consider the day of their appointment a day of celebration and ’Eid.”
Misbahul Mutahajjid, Page 680
