Musnad Ahmad 27:934

Hassan narrated to us, Zuhair narrated to us, from Abu Ishaq, from Mujahid, from Ibn Umar, who said: It was asked, "How many times did the Messenger of Allah, peace and blessings of Allah be upon him, perform Umrah?" He said, "Twice." Aisha said, "Ibn Umar knows that the Messenger of Allah, peace and blessings of Allah be upon him, performed Umrah three times, besides the Umrah which he combined with the Farewell Hajj."