Umar ya umurci sojojinsa da su ja da baya zuwa kan iyakar Larabawa, ya kuma fara tara runduna a Madina domin wani yakin neman shiga kasar Mesofotamiya .Umar ya nada Saad bn Abi Waqqas babban jami'i mai daraja.Saad ya bar Madina tare da sojojinsa a watan Mayu 636 ya isa Qadisiyyah a watan Yuni.Duk da yake Heraclius kaddamar da m a watan Mayu 636, Yazdegerd ya kasa muster sojojinsa a lokaci don samar da Byzantines tare da Farisa goyon baya.Umar da ake zargin yana sane da wannan kawancen, ya yi amfani da wannan gazawar: bai so ya yi kasadar yaki da manyan kasashe guda biyu a lokaci guda ba, sai ya yi gaggawar matsawa ya karfafa sojojin musulmi a Yarmouk don shiga tare da fatattakar Rumawa.A halin da ake ciki, Umar ya umarci Saad da ya shiga tattaunawar sulhu da Yazdegerd na uku tare da gayyatarsa ​​ya musulunta don hana sojojin Farisa shiga filin.Heraclius ya umurci janar Vahan kada ya shiga yaƙi da Musulmai kafin samun umarni bayyananne;duk da haka, saboda tsoron karin dakarun Larabawa, Vahan ya kai wa sojojin musulmi hari a yakin Yarmouk a watan Agusta 636, kuma aka fatattake su.Da barazanar Rumawa ta kawo karshe, daular Sassanid har yanzu tana da karfin gaske mai tarin tarin ma’aikata, kuma nan da nan Larabawa suka sami kansu suna fuskantar wata babbar runduna ta Farisa dauke da dakaru daga kowane lungu na daular, ciki har da giwayen yaki, kuma manyan hafsoshinta suka ba da umarni. .A cikin watanni uku, Saad ya ci sojojin Farisa a yakin al-Qādisiyyah, wanda ya kawo karshen mulkin Sassanid a yammacin Farisa daidai.Ana kallon wannan nasara a matsayin wani muhimmin juzu'i a ci gaban Musulunci: