The command to fight the people until they say "La ilaha illallah Muhammad Rasul-Allah", and establish Salat, and pay the Zakat, and believe in everything that the prophet (ﷺ) brought. Whoever does that, his life and his wealth are protected except by its right, and his secrets are entrusted to Allah, the most high. Fighting those who withhold Zakat or other than that is one of the duties of Islam and the Iman should be concerned with the Laws of Islam
Abu Burda reported Allah's Messenger (ﷺ) as saying:
There would come people amongst the Muslims on the Day of Resurrection with as heavy sins as a mountain, and Allah would forgive them and He would place in their stead the Jews and the Christians. (As far as I think), Abu Raub said: I do not know as to who is in doubt. Abu Burda said: I narrated it to 'Umar b. 'Abd al-'Aziz, whereupon he said: Was it your father who narrated it to you from Allah's Apostle (ﷺ)? I said: Yes.
Reference: Sahih Muslim 2767 d In-book : Book 50, Hadith 60 USC-MSA web (English) : Book 37, Hadith 6668 (deprecated)
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