There are 5 Tenets (pillars or principles) of Islam, (i) Shahadah (Iman - faith), (ii) Salah (Distinctive Submission - a form of Islamic Prayer ), (iii) Zakah (Islamic Charity), (iv) Sawm (Islamic Fasting), (v) Hajj (Pilgrimage to Makkah).
It is in Hadith - Narrated by Ibn Umar (رضئ اللہ تعالی عنہ) - Allah's Apostle (صلى الله عليه و آله وسلم) said - Islam is based on (the following) five (principles) - (i) 'there is no (real) god except Allah (سبحانه و تعالى) and Mohammad (صلى الله عليه و آله وسلم) is Allah's Apostle, (ii) to offer Salah ( prayers) dutifully and perfectly, (iii) to pay Zakat (Islamic charity), (iv) to perform Hajj (Pilgrimage to Makka), and (v) to observe fast during the month of Ramadhan. (Bukhari Book 2 Hadith 7 )
Hajj is the fifth pillar of Islam. It is obligatory for all Muslims, who can afford and travel, to do Hajj at least once in their lifetime.
Hajj is performed during the period from the 8th to 13th Dhu'l Hijjah, every lunar year.
Hajj is the annual assembly of Muslims from all parts of the world in which all barriers of language, territory, color and race disappear and the bond of faith becomes apparent. There are a number of benefits of Hajj to people, individually as well as collectively. Please refer concerned books for details.
It is in Quran - وَلِلَّهِ عَلَى النَّاسِ حِجُّ الْبَيْتِ مَنِ اسْتَطَاعَ إِلَيْهِ سَبِيلًا ۚ وَمَن كَفَرَ فَإِنَّ اللَّهَ غَنِيٌّ عَنِ الْعَالَمِينَ [ Hajj to the House (Ka’bah) is a duty that mankind owes to Allah, those who can afford the expenses. Whoever disbelieves, then Allah stands not in need of any of the Aalameen (Mankind and Jinns)." (Aal-e-Imran - 97)It is in Hadith - Narrated Abu Huraira (رضئ اللہ تعالی عنہ) - The Prophet (صلى الله عليه و آله وسلم) said, "Whoever performs Hajj for Allah's sake and does not have sexual relations with his wife, and does not do evil or sins then he will return (after Hajj free from all sins) as if he were born anew.” (Bukhari, Muslim )It is in Hadith - Narrated Abu Huraira (رضئ اللہ تعالی عنہ) - The Prophet (صلى الله عليه و آله وسلم) was asked, "Which is the best deed?" He said, "To believe in Allah and His Apostle." He was then asked, "Which is the next (in goodness)?" He said, "To participate in Jihad in Allah's (سبحانه و تعالى) Cause." He was then asked, "Which is the next?" He said, "To perform Hajj-Mabrur. (Bukhari )