According to Shia Muslims, on the 18th of Dhu al-Hijjah, at a place known as Ghadir Khumm, Muhammad gathered all Muslims and made a speech following a revelation during his final Hajj pilgimage in the last year of his life, where he said "Whomsoever to him I am master (Maula), Ali is also his/her master (Maula). O God, love those who love him, and be hostile to those who are hostile to him".
The event of Ghadir Khumm has been revealed in both Shia and Sunni sources. Sunnis, however, do not believe that there was any appointment of a successor.
Shia observe the date Fasting, doing Ghusl (ritual bath), reciting Du'a Nudba and giving food to believers.
