Musnad Ahmad 937:132

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Ibrahim al-Taymi, from his father, from Abu Dharr, who said: I said: "O Messenger of Allah, which mosque was placed on the earth first?" He said: "The Sacred Mosque (al-Masjid al-Haram)." I said: "Then which?" He said: "Then the Furthest Mosque (al-Masjid al-Aqsa)." Abu Mu'awiyah said: Meaning Bayt al-Maqdis (Jerusalem). I said: "How much was between them?" He said: "Forty years. And wherever the prayer overtakes you, pray, for it is a mosque."