ays i ▁trib al ▁fa ction , ▁he ▁maintained ▁his ▁alleg iance ▁to ▁the ▁Um ay y ads ▁under ▁Mar wan ▁I ▁( r . ▁ 6 8 4 – 6 8 5 ) ▁and ▁the ▁latter ' s ▁son ▁Abd ▁al - Mal ik ▁( r . ▁ 6 8 5 – 7 0 5 ) ▁following ▁the ▁dev ast ating ▁Q ays i ▁defeat ▁in ▁the ▁Battle ▁of ▁Mar j ▁Rah it ▁at ▁the ▁hands ▁of ▁the ▁Um ay y ads ▁and ▁their ▁Yam ani ▁al lies , ▁particularly ▁the ▁Ban u ▁Kal b ▁tribe . ▁However , ▁the ▁battle ▁still ▁left ▁him ▁and ▁his ▁tribes men ▁bitter ▁toward ▁their ▁Kal bi ▁riv als ▁and ▁the ▁Um ay y ads , ▁and ▁this ▁became ▁apparent ▁during ▁the ▁Battle ▁of ▁Kh az ir ▁in ▁ 6 8 6 . ▁During ▁that ▁eng agement , ▁Um ay r ▁commanded ▁the ▁left ▁wing ▁of ▁the ▁Um ay y ad ▁army ▁led ▁by ▁U bay d ▁Al lah ▁ibn ▁Z iy ad ▁against ▁the ▁pro - Al id ▁forces ▁led ▁by ▁I bra him ▁ibn ▁al - As ht ar ; ▁before ▁the ▁two ▁sides ▁met , ▁Um ay r ▁secret ly ▁met ▁with ▁I bn ▁al - As ht ar ▁and ▁offered ▁to ▁defect ▁with ▁his ▁Q ays i - domin ated ▁regiment ▁in ▁the ▁middle ▁of ▁battle . ▁The ▁result ▁was ▁an ▁Um ay y ad ▁rout ▁and ▁U bay d ▁Al lah ' s ▁sl ay ing . ▁Um ay r ▁was