1.    When Hajj was prescribed:   

According to the correct view, Hajj was made obligatory in 9AH, the year of the Delegations (al-Wufood), in which Soorat Aal ‘Imraan was revealed, in which Allaah says (interpretation of the meaning):  

“And Hajj (pilgrimage to Makkah) to the House (Ka’bah)is a duty that mankind owes to Allaah, those who can afford the expenses (for one’s conveyance, provision and residence).” [Aal ‘Imraan 3:97]  

The ruling of Hajj:

          Hajj is a fareedah (obligatory duty), one of the pillars of Islam. The evidence (daleel) for this is the aayah mentioned above, and there is also evidence in the Sunnah which indicates the same thing.

          Ibn ‘Umar (may Allaah be pleased with them both) said: the Messenger of Allaah (sallallaahu álayhi wa sallam) said: “Islam is built upon five (pillars): testifying that none deserves to be worshipped but Allaah and that Muhammad is the Messenger of Allaah, establishing regular prayer, paying zakaah, Hajj and fasting Ramadhaan.” ( Al-Bukhaari, 8; Muslim, 16).