Musnad Ahmad 30:2885

Waki' narrated to us, from Sufyan, from Salih, the freed slave of al-Taw'amah, from Abu Hurayrah, who said: The Messenger of Allah (peace and blessings of Allah be upon him) said: "A prayer in my mosque is better than a thousand prayers in any other mosque, except for the Sacred Mosque (al-Masjid al-Haram)."