Then there is the Battle of Nahawand where in 21 AH, the Iranian forces began preparations to fight the Muslims in the Ajam of Iraq, i.e., the part of Iraq which belonged to the Persians. In order to regain control of the lands conquered by the Muslims, 150,000 Iranian warriors had gathered in opposition to them in Nahawand.
Hazrat Sa‘d (ra) informed Hazrat Umar (ra) about this and after taking counsel from those of experience and understanding, he appointed an Iraqi, Hazrat Nu‘man bin Muqqarin Muzni (ra) as the commander of the Muslim army.
At the time, Hazrat Nu‘man (ra) was in Kaskar, which is situated between Nahrawan and the edge of the Tigris River near Busra and in which there were many towns and villages. So as it were, Hazrat Umar (ra) instructed him to reach Nahawand.
In comparison to the Iranian army of 150,000, the Muslim army comprised of only 30,000. Whilst passing through the ranks of the army, Hazrat Nu‘man (ra) gave certain instructions and said that if he was to be killed, Huzaifah would take command of the army and if he too were to be slain, then so and so would be handed command of the army. In doing so, he named seven individuals one after the other.
Thereafter, he supplicated to God Almighty saying, “O Allah, grant honour to Your religion, help Your servants and grant the rank of martyrdom to Nu‘man first and foremost.” According to another narration, he prayed, “O Allah, I pray You grant me the pleasure of my eyes through such a victory in which lies the honour of Islam and my martyrdom.” When the battle commenced, the Muslims fought with such bravery that they had conquered the battlefield before the sun could even set and in this battle Hazrat Nu‘man (ra) was martyred.
Abu Lu‘lu Feroz was captured in this battle and was given as a slave to Hazrat Mughira bin Shu‘bah (ra). This is the same person who later attacked Hazrat Umar (ra) and martyred him. Hazrat Umar (ra) wrote a letter to the Amir of Nahawand stating that if God Almighty was to grant victory to the Muslims, then the khumus (1/5) of the spoils of war should be set aside for the treasury and the rest should be distributed amongst the Muslims. But if this army was to be defeated, then the belly of the earth was better than what lay above it, i.e., the grave.