You've not specified the reasons why the PIC should be stopped (or indeed your definition of 'Stop', or how quickly it should happen, or the state of the PIC when it is stopped), so to experiment, why not simply start with...

Code:
	LED var PortB.1
	StopPin var PortB.0

	TRISB=%00000001

Loop:	Toggle LED
	Pause 500
	While StopPin=1:Wend
	Goto Loop