The day that marks the event you are referring to is known as "Ghadir Khum." It is a significant event for the Shia Muslim community and is celebrated by them as a day of commemoration and reverence. Ghadir Khum marks the occasion when the Prophet Muhammad (PBUH) made the statement I mentioned earlier during his final sermon. This event holds great importance in the Shia tradition as evidence for the leadership and succession of Ali ibn Abi Talib. On Ghadir Khum, Shia Muslims celebrate and reflect upon Ali's role in the history of Islam. It is important to note that the commemoration and significance of Ghadir Khum differ among different Islamic sects, with the Shia community giving it greater emphasis.