Musnad Ahmad 25:1110

Al-Zubayri Muhammad ibn Abdullah ibn al-Zubayr narrated to us, Sharik narrated to us, from Simak, from Ikrimah, from Ibn Abbas, from the Prophet, peace and blessings be upon him, who said: "Upon every Muslim is a Hajj. And if I were to say: every year, it would have been [obligatory]."