Volume 4, Book 55, Number 636:
Narrated 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.”