Musnad Ahmad 788:147

Abu Mu'awiyah narrated to us, Al-A'mash narrated to us, from Shaqiq, from Abu Musa, who said: The Messenger of Allah, peace and blessings of Allah be upon him, was asked about a man who fights out of bravery, a man who fights out of zeal, and a man who fights for show—which of those is in the way of Allah the Exalted? The Messenger of Allah, peace and blessings of Allah be upon him, said: "Whoever fights so that the word of Allah may be supreme, then he is in the way of Allah the Almighty and Majestic."