Musnad Ahmad 25:439

'Affan narrated to us, Wuhayb narrated to us, Ayyub narrated to us, from Ibn Abi Mulaykah, who said: 'Urwah said to Ibn 'Abbas: "Until when will you lead people astray, O Ibn 'Abbas?" He said: "What is that, O 'Urayyah?" He said: "You command us to perform 'Umrah during the months of Hajj, while Abu Bakr and 'Umar forbade it." Ibn 'Abbas said: "The Messenger of Allah, peace and blessings of Allah be upon him, performed it." 'Urwah said: "They were both more following of the Messenger of Allah, peace and blessings of Allah be upon him, and more knowledgeable of him than you."