What is the ruling on spoils acquired by a group of non-Muslims fighting alone?

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If a group of non-Muslims fights alone and acquires spoils, one opinion suggests the spoils belong entirely to them with no one-fifth being taken, because this acquisition is permissible (mubah) and not done under the context of Jihad, thus resembling gathering firewood or fodder which are entirely for the gatherer. The opposing view is that the one-fifth deduction should be taken, and the remainder belongs to them, as this bounty originated from the territory of the people of Islam, making it analogous to the spoils acquired by Muslims.