Sahih Muslim Book 7, Hadith Number 3209.

Chapter : The merit of praying in the two mosques, at Mecca and Medina.

Abu Huraira (Allah be pleased with him) narrated It directly from Allah’s Apostle'(may peace be upon him) having said this: A prayer in my mosque is a thousand times more excellent than a prayer in any other mosque, except Masjid al-Haram (Mosque of the Ka’ba).