Narrated Abu Sa'eed:
that the Messenger of Allah (ﷺ) said: "When you see a man frequenting the Masjid, then testify to his faith. Indeed Allah, Most High, said: The Masjid shall be maintained by those who believe in Allah and the Last day (9:18)." (JA)
English reference (JA): Vol. 5, Book 44, Hadith 3093 (JA)
Arabic reference (JA): Book 47, Hadith 3375 (JA)