Musnad Ahmad 33:282

Abu Mu'awiyah narrated to us, Hajjaj ibn Arta'ah narrated to us, from Muhammad ibn al-Munkadir, from Jabir ibn Abdullah, who said: A Bedouin came to the Prophet, peace and blessings of Allah be upon him, and said: "O Messenger of Allah, inform me about the Umrah: is it obligatory?" The Messenger of Allah, peace and blessings of Allah be upon him, said: "No, and that you perform Umrah is better for you."