Musnad Ahmad 937:45

Sufyan narrated to us, from al-A'mash, from Ibrahim al-Taymi, from his father, from Abu Dharr, who said: I asked the Messenger of Allah, peace and blessings of Allah be upon him: "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)." I said: "How much was between them?" He said: "Forty years." I said: "Then which?" He said: "Then wherever the prayer overtakes you, pray, for it is all a mosque."