Sunan Ibn Majah, Chapter: The Chapters on the Mosques and the Congregations

"I said: 'O Messenger of Allah! Which masjid (mosque) was built first?' He said: 'Al-Masjid Al-Haram (in Makkah).' I said: 'Then which?' He said: 'Then Al-Masjid Al-Aqsa (in Jerusalem).' I said: 'How many years between them?' He said: 'Forty years, but the whole earth is a masjid (mosque) for you, so pray wherever you are when the time for prayer comes.'" (Sahih)