Musnad Ahmad 27:1835

Ibn Numayr narrated to us, al-A‘mash informed us, from Mujahid, who said: ‘Urwah ibn al-Zubayr asked Ibn ‘Umar: “In which month did the Messenger of Allah, may Allah bless him and grant him peace, perform ‘Umrah?” He said: “In Rajab.” ‘A’ishah heard us, so Ibn al-Zubayr asked her and informed her of what Ibn ‘Umar said. She said: “May Allah have mercy on Abu ‘Abd al-Rahman. The Messenger of Allah, may Allah bless him and grant him peace, did not perform an ‘Umrah that I did not witness, and he never performed an ‘Umrah except in Dhu al-Hijjah.”