Book 24, Hadith 1

It was narrated that Abu Hurairah said:"The Messenger of Allah addressed the people and said: 'Allah, the Mighty and Sublime, has enjoined upon you Hajj.' A man said: 'Every year?' He remained silent until he had repeated it three times. Then he said: 'If I said yes, it would be obligatory, and if it were obligatory you would not be able to do it. Leave me alone so long as I have left you alone. Those who came before you were destroyed because they asked too many questions and differed with their prophets. If I command you to do something then follow it as much as you can, and if I forbid you to do something then avoid it