Is the Friday prayer (Jumu'ah) valid if performed in a usurped location?

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The Friday prayer is valid even if the mosque or part of its location is usurped, according to Ahmad ibn Hanbal. This allowance is made because the Friday prayer is specific to a certain location. If the Imam performs it in the usurped area and people refrain from praying there due to the usurpation, they miss the Jumu'ah. Similarly, if only some refrain, they miss it. For this reason, prayer behind Khawarij (seceders) and innovators is permitted. Furthermore, the prayer is valid in public roads and the courtyards (rihab) of the mosque due to necessity, and similarly for Eid prayers and funeral prayers.