And proclaim to mankind the Hajj
( pilgrimage ).
They will come to you on foot and on every lean camel,
they will come from every deep and distant (wide) mountain highway
(to perform Hajj).
(Al-Hajj 22:27)

و حدثني ‏ ‏زهير بن حرب ‏ ‏حدثنا ‏ ‏يزيد بن هارون ‏ ‏أخبرنا ‏‏الربيع بن مسلم القرشي ‏ ‏عن ‏ ‏محمد بن زياد ‏ ‏عن ‏ ‏أبي هريرة ‏ ‏قال ‏
خطبنا رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏فقال أيها الناس قد ‏ ‏فرض الله عليكم الحج فحجوا فقال رجل أكل عام يا رسول الله فسكت حتى قالها ثلاثا فقال رسول الله ‏ ‏صلى الله عليه وسلم ‏ ‏لو قلت نعم لوجبت ولما استطعتم ثم قال ‏ ‏ذروني ‏ ‏ما تركتكم فإنما هلك من كان قبلكم بكثرة سؤالهم واختلافهم على أنبيائهم فإذا أمرتكم بشيء فأتوا منه ما استطعتم وإذا نهيتكم عن شيء فدعوه ‏
)صحيح مسلم(

Abu Huraira (Allah be pleased with him) reported:
Allah's Messenger
(may peace be upon him)
addressed us and said: O people,
Allah has made hajj obligatory for you;
so perform hajj. Thereupon a person said: Messenger of Allah,
(is it to be performed)
every year?
He (the Holy Prophet) kept quiet, and he repeated (these words) thrice,
whereupon Allah's Messenger (may peace be upon him) said:
If I were to say" yes," it would become obligatory
(for you to perform it every year) and you would not be able to do it.
Then he said: Leave me with what I have left to you,
for those who were before you were desroyed because of
excessive questioning, and their opposition to their apostles.
So when I command you to do anything, do it as
much as it lies in your power and when I forbid you to do anything,
then abandon it