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
Anas b. Malik reported that Allah's Messenger (ﷺ) came to a woman who had been weeping for her (dead) child, and said to her:
Fear Allah and show endurance. She (not recognising him) said: You have not been afflicted as I have been. When he (the Holy Prophet) had departed, it was said to her that he was the Messenger of Allah (ﷺ), she was mortally shocked. She came to his door and she did not find doorkeepers at his door. She said: Messenger of Allah. I did not recognise you. He said: Endurance is to be shown at first blow, or at the first blow.
Reference: Sahih Muslim 926 b In-book : Book 11, Hadith 18 USC-MSA web (English) : Book 4, Hadith 2013 (deprecated)
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