Musnad Ahmad 33:1154

Ahmad ibn Abd al-Malik narrated to us, Ubayd Allah narrated to us, from Abd al-Karim, from Ata, from Jabir ibn Abdullah, who said: 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 for the Sacred Mosque (al-Masjid al-Haram). And a prayer in the Sacred Mosque is better than a hundred thousand prayers in any other."