Complex sentence: Eid al-Ghadeer is a festive day observed by Shia Muslims on the 18th of Dhu al-Hijjah in the Islamic calendar to commemorate the appointment of Ali ibn Abi Talib by the Islamic prophet Muhammad as his immediate successor, as per Shia belief.
Split into simpler sentences: Eid al-Ghadeer is a festive day observed by Shia Muslims on the 18th of Dhu al-Hijjah in the Islamic calendar. This day is to commemorate the appointment of Ali ibn Abi Talib by the Islamic prophet Muhammad as his immediate successor, as per Shia belief.