The Battle of Nihawand
By 21 AH / 642 CE, the Arabs had won several battles in Iraq and Persia, but the Sassanid Empire had not yet been broken — it had retreated and regrouped. Caliph Umar recognized that a decisive campaign was needed. He appointed al-Nu’man ibn Muqarrin to command the Muslim forces and mustered a substantial army.
The Sassanid forces at Nihawand (a site in western Iran) were large — estimates vary widely in the sources, from tens of thousands to over 100,000. The battle was three days long. The result was a decisive Muslim victory that shattered the Sassanid military capacity permanently.
The Prayer and the Death
Before the battle, al-Nu’man is reported to have made a specific prayer: “O God, grant me martyrdom today, in the moment of victory for the Muslims.” His prayer was answered exactly as he asked: he was killed in the battle, during the final push of the Muslim advance.
The command passed to Hudhaifa ibn al-Yaman (who had been designated as second commander), who concealed al-Nu’man’s death from the troops until after the battle was won — to prevent demoralization.
Fath al-Futuh
The Arabs called Nihawand fath al-futuh — “the opening of all openings.” The phrase reflects the understanding that with Nihawand, Iran was truly open: no organized Sassanid army would again oppose the Muslim advance. The emperor Yazdegerd III fled and was eventually killed by a miller, ending the dynasty.
See also: Seerah Miqdad Ibn Amr, Seerah Jabir Ibn Samurah, Seerah Al Mughira Ibn Shuba, Seerah Amr Ibn Al Jumuh, Quran Compilation History