How to ask for a reference when you’re not sure that you're applying yet
I would tell them this.


  I'm thinking about applying to a master's program and for a scholarship.  The deadline is the end of January, so I have to decide
  soon.  If I decide to apply, would you be willing to provide a letter
  of reference?
  
  Here are the links: ...
  
  I've also attached copies of my unofficial transcript and my resume.  You
  have my permission to discuss any of this in any letter you decide to write.


Most of your instructors will likely have acted as references in the past and if it's just an LOR you need, they know how to do that.  Give links to  the program and scholarship pages so they can confirm the details of what's required.