Muharram and the Day of Ashura for Shīʿa Muslims commemorate the martyrdom of Ḥusayn ibn ʿAlī, brother of Ḥasan and grandson of Muhammad, who was killed by Yazid ibn Muawiyah in Karbala (central Iraq). Ashura is a day of deep mourning which occurs on the 10th of Muharram. Arba'een commemorates the suffering of the women and children of Ḥusayn ibn ʿAlī's household. After Ḥusayn was killed, they were marched over the desert, from Karbala (central Iraq) to Shaam (Damascus, Syria). Many children (some of whom were direct descendants of Muhammad) died of thirst and exposure along the route. Arbaein occurs on the 20th of Safar, 40 days after Ashura. Mawlid, Muhammad's birth date. Unlike Sunnī Muslims, who celebrate the 12th of Rabi' al-awwal as Muhammad's day of birth or death (because they assert that his birth and death both occur in this week), Shīʿa Muslims celebrate Muhammad's birthday on the 17th of the month, which coincides with the birth date of Jaʿfar al-Ṣādiq, the 6th Shīʿīte Imam. Fāṭimah's birthday on 20th of Jumada al-Thani. This day is also considered as the "'women and mothers' day" ʿAlī's birthday on 13th of Rajab. Mid-Sha'ban is the birth date of the 12th and final Twelver imam, Muhammad al-Mahdi. It is celebrated by Shia Muslims on the 15th of Sha'aban. Laylat al-Qadr, anniversary of the night of the revelation of the Quran. Eid al-Mubahila celebrates a meeting between the Ahl al-Bayt (household of Muhammad) and a Christian deputation from Najran. Al-Mubahila is held on the 24th of Dhu al-Hijjah. Holy sites After the four holy cities of Islam (Mecca, Medina, Jerusalem, and Damascus), the cities of Najaf, Karbala, and Qom are the most revered by Shīʿa Muslims. The Sanctuary of Imām ʿAlī in Najaf, the Shrine of Imam Ḥusayn in Karbala, and the Shrine of Fāṭimah al-Maʿṣūmah in Qom are very essential for Shīʿa Muslims. Other venerated pilgrimage sites include the Imam Reza shrine in Mashhad, the Kadhimiya Mosque in Kadhimiya, Al-Askari Mosque in Samarra, the Sahla Mosque, the Great Mosque of Kufa, the Jamkaran Mosque in Qom, and the Tomb of Daniel in Susa. Most of the Shīʿa sacred places and heritage sites in Saudi Arabia have been destroyed by the Al Saud-Wahhabi armies of the Ikhwan, the most notable being the tombs of the Imams located in the Al-Baqi' cemetery in 1925. In 2006, a bomb destroyed the shrine of Al-Askari Mosque.