Eid Milad-un-Nabi, also known as Mawlid al-Nabi al-Sharif, Nabi Day, or Mawlid, is an Islamic festival that marks the birth anniversary of Prophet Muhammad. The festival is celebrated on different days by the Shia and Sunni sects, and the date of the festival changes every year as per the Muslim calendar called the Hijri calendar, which is based on the moon. The festival is observed in Rabi al-Awwal, the third month in the Islamic calendar, and is marked on the 12th day of Rabi ul-awwal by Sunni scholars, while some Shia scholars regard the 17th Rabi al-awwal as the accepted date.

The origin of celebrating Eid Milad-un-Nabi can be traced back to the early days of Islam when people used to gather and read verses to honor the prophet. The festival serves as an opportunity for people of the Muslim community to remember and honor Prophet Muhammads life and what he stood for. Muslims celebrate the day by remembering Prophet Muhammads teachings, offering special prayers, preparing sweet delicacies, and decorating their houses. The festival is also widely observed in many countries, including Sri Lanka, the United Kingdom, Pakistan, Bangladesh, Russia, and Germany, and in most Muslim-majority countries, the festival is recognized as a national holiday.

In summary, Eid Milad-un-Nabi is an Islamic festival that marks the birth anniversary of Prophet Muhammad, observed in Rabi al-Awwal, the third month in the Islamic calendar, and celebrated on different days by the Shia and Sunni sects. The festival serves as an opportunity for people of the Muslim community to remember and honor Prophet Muhammads life and what he stood for.