Narrated Abu Dhar: I said, "O Allah's Apostle! Which mosque was first built on the surface of the earth?" He said, "Al- Masjid-ul-,Haram (in Mecca)." I said, "Which was built next?" He replied "The mosque of Al-Aqsa (in Jerusalem) ." I said, "What was the period of construction between the two?" He said, "Forty years." He added, "Wherever (you may be, and) the prayer time becomes due, perform the prayer there, for the best thing is to do so (i.e. to offer the prayers in time).

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."