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Abu Musa reported: A man came to the Prophet, peace be upon him, and said, “O Messenger of Allah, what is fighting in the cause of Allah? Some of us fight out of anger and others out of zeal.” He raised his head and said, “He who fights so that the word of Allah is made high is fighting in the cause of Allah the Exalted.”
[Sahih Bukhari, Book 3, Number 125]

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