4. A Fundamental Institution

Hajj is one of the pillars of Islam and is an incumbent religious duty to be performed once in a lifetime by every able Muslim.

Anyone who denies it's being obligatory is deemed a non- believer, outside of Islam. 

Allah Subhanahu Wa Ta’ala states:

Wa lilaahi 'alannaasi Hij-jul- Bayti manistataa-'ailay-hi sabiila. Wa man- kfara fa-'in-nallaha Ganiy-yun 'anil aalamin.

"And pilgrimage to the house [i.e. is the Ka'bah] is a duty unto Allah incumbent upon those who have the ability for it. As for him who disbelieves, [let him know that] Allah is independent of all creation."

And in the words of Prophet Muhammad salallahu ‘alayhi wa sallam  :
"O mankind, hajj has been made obligatory for you, so perform Hajj."

"Islam is that you bear a witness that there is no deity except Allah and that Muhammad is the messenger of Allah [and that you] establish prayer and gives zakah and fast during Ramadhan and make the pilgrimage to the house of Allah if you find a way thereto."