Holy Prophet Muhammad al-Mustafa (s.a.w.a.) said
The day of Ghadir Khumm is the best 'Eid of my nation. It is the day on which Allah, the High, ordered me to mention the appointment of my brother, Amir al-Mu'minin Imam ‘Ali ibn Abi Talib (a.s.) as the flag and standard of my nation.
- Al-Amali of As-Saduq, Page 125, Hadith 8 -