Nafi' narrates: Sayyiduna Abdullah bin Umar (may Allah be pleased with them both) was asked: "Where did the Prophet (peace and blessings be upon him) offer prayer on the occasion of the Battle of the Confederates?" He replied: "The Prophet (peace and blessings be upon him) offered prayer in the middle of the low ground, beside an old ruined building that was there. The Prophet (peace and blessings be upon him) had given the people permission to go back; then he ordered me to call them, so I called them."
Al-Tabarani recorded it, and its narrators are thiqat (trustworthy).