Firstly: The command of Allah Ta‘ala. He says:
وَلِلَّهِ على الناس حج البيت من استطاع إليه سبيلا
Meaning: Whoever among the people has the means to do so is obligated, for the sake of Allah, to perform Hajj to that House.
Secondly: The hadith of the Prophet, sallallahu ‘alayhi wa sallam. He said:
(a) Islam is built upon five pillars:
(1) Testifying that there is no deity except Allah and that Muhammad, sallallahu ‘alayhi wa sallam, is the Messenger of Allah,
(2) Establishing Salah,
(3) Giving Zakah,
(4) Observing Sawm during the month of Ramadan, and
(5) Performing Hajj to the Sacred House of Allah. (Bukhari)
(b) O people! Allah has made Hajj obligatory upon you, so perform Hajj. (Muslim)
(Surah Aal ‘Imran: 97)