▁his ▁son ▁al - F ad l ▁ibn ▁al - R abi ' ▁both ▁became ▁viz iers ▁after ▁the ▁dismiss al ▁of ▁their ▁riv als ▁who ▁previously ▁held ▁the ▁office . ▁This ▁division ▁and ▁the ▁rival ry ▁between ▁the ▁two ▁offices ▁was ▁strength ened ▁during ▁the ▁" S amar ra ▁period ", ▁when ▁the ▁office ▁of ▁ha j ib ▁began ▁to ▁be ▁occupied ▁by ▁Turkish ▁slave ▁soldiers ▁( gh il man , ▁sing . ▁gh ul am ), ▁whose ▁" background , ▁formation , ▁and ▁interests ▁differ ed ▁stark ly ▁from ▁those ▁of ▁the ▁b ureau cr atic ▁viz ier ". ▁Under ▁C ali ph ▁al - M ut aw ak kil , ▁the ▁Turkish ▁hij ab ▁It akh ▁served ▁as ▁chief ▁minister , ▁since ▁the ▁C ali ph ▁did ▁not ▁nomin ate ▁a ▁viz ier . ▁ ▁In ▁the ▁late ▁ 9 th ▁century , ▁the ▁position ▁of ▁the ▁viz ier ▁was ▁strength ened , ▁as ▁the ▁powers ▁of ▁the ▁office ▁became ▁more ▁formal ized ▁and ▁he ▁emer ged ▁as ▁the ▁head ▁of ▁the ▁civil ian ▁administration , ▁under p inned ▁by ▁a ▁highly ▁special ized ▁secret arial ▁class . ▁Another ▁cont ender ▁for ▁authority ▁also ▁emer ged ▁in ▁the ▁commander - in - ch ief ▁of ▁the ▁army . ▁However , ▁the ▁ha j ib ▁remained ▁a ▁powerful ▁official , ▁especially ▁during ▁palace ▁cou ps , ▁as ▁he ▁controlled ▁a ▁part ▁of ▁the ▁cal i phal ▁body guard , ▁not ably ▁the ▁Ma ṣ ā ff iy ya . ▁Under ▁al