TgJ Is21:7 :וְעִמֵיה זוֹג פָרָשִין רָכֵיב עַל חְמָר רָכֵיב עַל גְמָל‏ : a pair of horsemen along with it: a rider on an ass and a rider on a camel
See the entire entry for rkb vb. to mount