Qatada قتادة · The Book on Faith

that the Messenger of Allah (ﷺ) said: "If you see a man who comes to the Masjid then bear witness to his faith." Because Allah, the Exalted, says: Only those who believe in Allah, and the Last Day, and establish the Salat, and give the Zakat (should) maintain the Masajid until the end of the Ayah (9:18)

that the Messenger of Allah (ﷺ) said: "Verbally abusing a Muslim is disobedience and fighting him is disbelief."