Musnad Ahmad 27:1328

Muhammad ibn Ubayd narrated to us, Ubayd Allah narrated to us, from Nafi’, from Ibn Umar, that the Messenger of Allah (peace and blessings of Allah be upon him) said: "A prayer in this mosque of mine is better than a thousand prayers in any other, except the Sacred Mosque (al-Masjid al-Haram)."