An gwabza yakin Ullais ne tsakanin sojojin Daular Rashidun da Daular Farisa ta Sassanid a tsakiyar watan Mayun shekara ta 633 Miladiyya a kasar Iraki , kuma a wasu lokuta ana kiranta Yakin Kogin Jini tun da sakamakon yakin an yi ta samun nasara. An kashe kiristoci masu yawa na Sassani da Larabawa.Wannan shi ne karo na karshe daga cikin yakoki hudu a jere da aka gwabza tsakanin musulmi mamaya da sojojin Farisa.Bayan kowane yaqi, Farisawa da kawayensu suka sake haduwa suka sake fafatawa.Waɗannan yaƙe-yaƙe sun haifar da ja da baya da sojojin Farisa Sassanid suka yi daga ƙasar Iraƙi tare da kame su a hannun musulmi a ƙarƙashin Halifancin Rashidun.