Sahih Bukhari
Sahih Bukhari Volume 004, Book 055, Hadith Number 636.
Hadith Section/Book: Sahih Bukhari Sahih Bukhari Book 55. Prophets
Narated By Abu Dhaar : I said, "O Allah's Apostle! Which mosque was built first?" He replied, "Al-Masjid-ul-Haram." I asked, "Which (was built) next?" He replied, "Al-Masjid-ul-Aqs-a (i.e. Jerusalem)." I asked, "What was the period in between them?" He replied, "Forty (years)." He then added, "Wherever the time for the prayer comes upon you, perform the prayer, for all the earth is a place of worshipping for you."