Musnad Ahmad 27:967

'Affan narrated to us, Hammad ibn Salamah narrated to us, Habib—meaning al-Mu'allim—informed us, from 'Ata', from 'Urwah ibn al-Zubayr, that he asked Ibn 'Umar: "Did the Messenger of Allah, may Allah bless him and grant him peace, perform 'Umrah in Rajab?" He said: "Yes." Then he informed 'Aishah of that, and she said: "May Allah have mercy on Abu 'Abd al-Rahman. The Messenger of Allah, may Allah bless him and grant him peace, never performed an 'Umrah except that he [Ibn 'Umar] was with him, and the Messenger of Allah, may Allah bless him and grant him peace, never performed an 'Umrah in Rajab at all."