How to stop workflow running twice on a record

How to stop workflow running twice on a record

Hi 

I have a workflow as below

Trigger: Lead record is created/edited - Repeat this workflow whenever a lead is edited is NOT TICKED 
Condition: When Lead Stage is MQL 
Action: Reassign Lead, Create Task

If the Lead goes into stage MQL, and then it changes to something else (this could be someone doing it by accident) and then back into MQL, the workflow rule is running twice. So there's 2 tasks, and the Lead is reassigned to someone else 

Is there a way I can stop this from happening? So that it would only execute the first time a Lead is in stage MQL? I don't want to have a task for every time it's there.

Thank you :)