 Hormuzan broke peace agreement three time and each time was pardoned by Caliph Umar and the peace renewed, until the third time when on Umar's instructions his capital was besieged and he was taken prisoner and sent to Madinah to umar, where he apparently accepted Islam.He later allegedly masterminded Umar's assassination.In 641 Persians under Yazdegerd III managed to muster up a massive army to attack Iraq, this army was defeated in Battle of Nahāvand in December 642.