The Messenger of Allah said: "If you see a man frequenting the mosques, then bear witness to his faith. Allah says: 'The mosques of Allah shall be maintained only by those who believe in Allah and the Last Day. [At-Taubah: 18]'" (Using translation from Ibn Mājah 802)   

عَنِ النَّبِيِّ ﷺ قَالَ إِذَا رَأَيْتُمُ الرَّجُلَ يَعْتَادُ الْمَسْجِدَ فَاشْهَدُوا لَهُ بِالْإِيمَانِ فَإِنَّ اللَّهَ يَقُولُ {إِنَّمَا يَعْمُرُ مَسَاجِدَ اللَّهِ مَنْ آمَنَ بِاللَّهِ} [التوبة 18]  

The Messenger of Allah ﷺ said:Whoever prays ʿIshaʿ in congregation, it will be like spending half the night in prayer (qiyam) and whoever prays ʿIshaʿ and Fajr in congregation, it will be like spending the whole night in prayer.ʿ (Using translation from Aḥmad 491)  

قَالَ رَسُولُ اللَّهِ ﷺ «مَنْ صَلَّى الْعِشَاءَ فِي جَمَاعَةٍ كَانَ كَقِيَامِ نِصْفِ لَيْلَةٍ وَمَنْ صَلَّى الْفَجْرَ فِي جَمَاعَةٍ كَانَ كَقِيَامِ لَيْلَةٍ»