Abu Dharr reported:

I said: Messenger of Allah, which mosque was set up first on the earth? He said: Al-Masjid al-Haram (the sacred). I (again) said: Then which next? He said: It was the Masjid Aqsa. I (again) said: How long the space of time (between their setting up)? He (the Prophet) said: It was forty years. And whenever the time comes for prayer, pray there, for that is a mosque; and in the hadith transmitted by Abu Kamil (the words are):" Whenever time comes for prayer, pray, for that is a mosque (for you)."

حَدَّثَنِي أَبُو كَامِلٍ الْجَحْدَرِيُّ، حَدَّثَنَا عَبْدُ الْوَاحِدِ، حَدَّثَنَا الأَعْمَشُ، ح قَالَ وَحَدَّثَنَا أَبُو بَكْرِ بْنُ أَبِي شَيْبَةَ، وَأَبُو كُرَيْبٍ قَالاَ حَدَّثَنَا أَبُو مُعَاوِيَةَ، عَنِ الأَعْمَشِ، عَنْ إِبْرَاهِيمَ التَّيْمِيِّ، عَنْ أَبِيهِ، عَنْ أَبِي ذَرٍّ، قَالَ قُلْتُ يَا رَسُولَ اللَّهِ أَىُّ مَسْجِدٍ وُضِعَ فِي الأَرْضِ أَوَّلُ قَالَ ‏"‏ الْمَسْجِدُ الْحَرَامُ ‏"‏ ‏.‏ قُلْتُ ثُمَّ أَىٌّ قَالَ ‏"‏ الْمَسْجِدُ الأَقْصَى ‏"‏ ‏.‏ قُلْتُ كَمْ بَيْنَهُمَا قَالَ ‏"‏ أَرْبَعُونَ سَنَةً وَأَيْنَمَا أَدْرَكَتْكَ الصَّلاَةُ فَصَلِّ فَهُوَ مَسْجِدٌ ‏"‏ ‏.‏ وَفِي حَدِيثِ أَبِي كَامِلٍ ‏"‏ ثُمَّ حَيْثُمَا أَدْرَكَتْكَ الصَّلاَةُ فَصَلِّهْ فَإِنَّهُ مَسْجِدٌ ‏"‏ ‏.‏