Musnad Ahmad 27:1976

Muhammad ibn Ubayd narrated to us, Abd al-Malik narrated to us, from Ata, from Ibn Umar, who said: The Messenger of Allah, may Allah bless him and grant him peace, said: "Indeed, prayer in this mosque of mine is better than prayer in any other mosque besides it, except for the Sacred Mosque (al-Masjid al-Haram)."