Complex sentence: His first expedition was to Raymah, where he quelled an insurgency and then fought in a battle against a prince called "Saheb bin Jayiash (Ar: صاحب بن جياش)," which ended with him beheading Saheb bin Jayiash and cutting off his hands.
Split into simpler sentences: His first expedition was to Raymah, where he quelled an insurgency. Subsequently, he then fought against "Saheb bin Jayiash (Ar: صاحب بن جياش),", a prince, which ended with the beheading of Saheb bin Jayiash and cutting off his hands.