The first mosque
Hadith: Hadrat Abu zar radhiAllahu anhu narrates that he asked: “Oh the prophet (sallallaahu alaihi wasallam) of Allah! Which mosque was constructed first on the earth? He the holy prophet sallallaahu alaihi wasallam said: “Mosque of Haram sharif”. I asked: “which one the next?” He, the prophet  sallallaahu alahihi wasallam said: “Next the Mosque of Aqsa”. I asked: “in between these two what would have been the period of time?” He, the prophet sallallaahu alaihi wasallam said: “Forty years.  And now the complete earth is a Mosque for you. Whenever the time arrives for prayers, then pray there.” (Bukhari sharif, Hadith: 3186)