Sayyiduna Abu Hurayrah (may Allah be pleased with him) says: The Messenger of Allah (peace and blessings be upon him) addressed us and said: "O people! Hajj has been made obligatory upon you, so perform Hajj." A man said: "Every year?" He (peace and blessings be upon him) remained silent until the man had said it three times. Then the Messenger of Allah (peace and blessings be upon him) said: "Had I said yes, it (performing Hajj every year) would have become obligatory, and you would not have been able to do it." Then he said: "Leave me alone as long as I leave you alone. Indeed, those before you were destroyed because of their excessive questioning and their disagreeing with their prophets. So when I command you to do something, do of it as much as you are able, and when I forbid you from something, leave it."
Hadith Referenceالسنن الكبرى للبيهقي / كتاب الحج / 8615