Hajj - The Fifth Pillar of Islam
Hajj is the fifth pillar of Islam. It is obligatory for every Muslim to perform Hajj once in his, or her, lifetime unless there is no financial or physical ability. Allah (swt) has said,

"Say: "Allah spoke the Truth: follow the religion of Abraham, the sane in faith; he was not of the Pagans." The first House (of worship) appointed for people was that at Bakkah; full of blessing and of guidance for all kinds of beings. In it are Signs manifest; (for example), the Station of Abraham; whoever enters it attains security; pilgrimage thereto is a duty people owe to Allah, those who can afford the journey; but if any deny faith, Allah stands not in need of any of His creatures." (2:96-97)

"And complete Hajj and 'Umrah in the service of Allah" (2:196)

"For Hajj are the months well-known. If any one undertakes that duty therein, let there be no obscenity, nor wickedness, nor wrangling in the Hajj and whatever good you do, (be sure) Allah knows it. And take a provision (with you) for the journey, but the best of provisions is right conduct. So fear Me, O you that are wise!" (2:198) 



The Prophet (S) said: 
"O people! Perform Hajj for Allah has made it obligatory on you". Hearing this, a man said, "is it every year O Messenger of Allah?" The Prophet (S) kept silent until the man repeated the question thrice and then said, "if I say yes it will become compulsory and you won't be able to do it". [Muslim and Ahmad]. Ibn 'Abbas (r) said,

"Allah's Messenger (S) addressed us saying, "O people! Allah has prescribed Hajj on you". Al-Aqra'a ibn Haabis then stood up and said, "is it for every year O Messenger of Allah?" The Prophet (S) replied, "if I say yes it would become obligatory and if it's obligatory to perform Hajj annually you certainly won't be able to do it. Hajj should be performed only once in one's lifetime and whoever does more, it will be considered supererogatory." [Related by An-Nassa'i, Abu Dawud, Ibn Maajah and Ahmad].