Bani Quraizah were a Jewish tribe who rebelled and betrayed their peace treaty with the Muslims during the Battle of the Trench. The Muslims laid siege to the tribe, this spot (where a masjid once stood) marks the place where the prophet (ﷺ) offered salat during the siege.
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References: Wikipedia, History of Madinah Munawwarah – Dr. Muhammad Ilyas Abdul Ghani