The conquest's decisive battles at al-Qadisiyyah and Nahavand are described in the surviving Arabic sources, written generations after the events they record, and the scholarship treats those figures with caution while narrating the fall of the Sasanian empire province by province, without ever totaling losses across the whole campaign.
What would resolve this A source critical study of the earliest surviving casualty claims for al-Qadisiyyah and Nahavand, combined with a historian's accounting of losses across the conquest's provincial campaigns.
OpenEarly Islamic history, Sasanian history, source criticism.Hugh Kennedy, The Great Arab Conquests: How the Spread of Islam Changed the World We Live In