Fiqh-us-Sunnah Volume 5, Hajj and ‘Umrah, Fiqh 5.001A.

The majority of the scholars hold that Hajj was prescribed in the sixth year after Hijrah (Migration of the Prophet (peace be upon him) from Makkah to Madinah) for it was then that the following verse concerning it was revealed: “And complete the Hajj and ‘Umrah in the service of Allah” (Qur’an 2.194). This conclusion is based on the understanding that the “completion” in the above verse in fact refers to the time when it was first made obligatory. This view is also supported by ‘Alqamah, Masrouq, and Ibrahim An-Nakh’i, who substitute “And establish” for “And complete” in the above verse, as reported by At-Tabarani on sound authority. Ibn-al-Qayyim, however, is inclined to the view that Hajj was made obligatory in the ninth or the tenth year of Hijrah.