It is narrated from Sayyiduna Ibn Abbas (may Allah be pleased with them both) that the Messenger of Allah (peace and blessings be upon him) said: "Hajj is obligatory upon every Muslim who has the means. If I had said 'every year,' then performing Hajj every year would have become obligatory."
Hadith Referenceمسند احمد / ومن مسند بني هاشم / 2969
Hadith Gradingحکم دارالسلام:صحيح، وهذا سند ضعيف، وهو مكرر: 2663