Al-Lu'lu Wal-Marjan 298 — The Book of Mosques and Places of Worship.

Abu Dharr Narrated from:

I said, "O Allâh's Messenger! Which mosque was first built on the surface of the earth?" He said, "Al-Masjid-ul-Harâm (at Makka).. " I said, "Which was built next?" He replied, "Al-Masjid-ul-Aqsa (at Jerusalem)." I said, "What was the period of construction between the two?" He said, "Forty years." He added, "Wherever (you may be, and) As-Salât (the prayer) time becomes due, perform As-Salât (the prayer) there, for the best thing is to do so [i.e. to offer Salât (prayers) in time]." ( Sahîh Al-Bukhârî, Hadîth No. 585, Vol. 4)