قَصْرُ صِفَةٍ عَلَى مَوْصُوفٍ
Restricting an attribute to a particular bearer.
لَا فَارِسَ إِلَّا عَلِيٌّ
There is no horseman except Ali.
The attribute of horsemanship is assigned exclusively to Ali within the intended scope. It does not deny Ali's other characteristics. Depending on context, the restriction may exclude all other horsemen in a specified reality or only a particular rival contemplated by the listener.