Sahih Muslim Book 7, Hadith Number 3213.

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

Ibn ‘Umar (Allah be pleased with them) reported Allah’s Apostle (may peace be upon him) as saying: Prayer in this mosque of mine is better than a thousand prayers (observed in other mosque.) besides it, except that of Masjid al-Haram.