The observance of the birthday of Islam founder Prophet Muhammad, which is celebrated in Rabi' al-awwal, the third month in the Islamic calendar. Shi’a Muslims celebrate it five days later than Sunni Muslims.

Source:
“Calendar of Observances.” Anti-Defamation League, 2019, www.adl.org/education/resources/tools-and-s.trategies/calendar-of-observances. Accessed 25 Sept. 2020