Musnad Ahmad 27:1782

Ishaq ibn Yusuf narrated to us, from Sharik, from Abu Ishaq, from Mujahid, from Ibn Umar, who said: "The Messenger of Allah (peace and blessings of Allah be upon him) performed Umrah twice before he performed Hajj." This reached Aisha, so she said: "The Messenger of Allah (peace and blessings of Allah be upon him) performed four Umrahs. Abdullah ibn Umar knows of that, one of them was with his Hajj."