In the Quran, Islam's revealed text, God says: "Thus We settled Abraham at the site of the House (the Ka'aba) (saying): 'Do not associate anything with Me, and purify My house for those who walk around it, and those who stand there (praying), and those who bow down on their knees in worship. Proclaim the pilgrimage among mankind: they will come to you on foot and on every lean (beast of burden); Let them come from every deep ravine, to bear witness to the advantages they have, and to mention God's name on appointed days." Chapter 22, Verses 26-28Hajj is one of the "five pillars" of the Islamic faith. (The other pillars include a declaration of faith, daily prayers, offering regular charity, and fasting during the month of Ramadan.) Pilgrimage is a once-in-a-lifetime obligation for those who have the physical and financial ability to undertake the journey. When the main portion of the pilgrimage is completed, Muslims worldwide gather for communal prayers on the first day ( October 15) of Eid ul-Adha ( EED-al-ODD-ha), the second of the two major Muslim holidays. The obligatory and optional activities of Hajj include: * Entrance into a state of self-control called "ihram," during which pilgrims are forbidden to harm living creatures, even insects or plants, or raise the voice in anger. The state of ihram is signified (for men) by the wearing of two pieces of unsown white cloth. This clothing signifies the equality of all before God. No specific clothing is prescribed for female pilgrims. * Circling ("Tawaf") of the "Ka'aba," the stone building Muslims believe was originally built by Abraham and his son Ishmael. The Ka'aba is viewed as the first sanctuary on earth dedicated to the worship of the One God. It is a symbol of unity for Muslims because all prayers, wherever they are performed, are oriented in the direction of the Ka'aba.