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)." (Another chain) from Abu Sa'eed from the Prophet (ﷺ) with similar wording except that he said: "Yata'ahadul Masjid."