Question: I am collaborating with a foreign author. As I am still pursuing my degree, I have to add my supervisor's name in that paper, even though my supervisor has not contributed to the preparation of this manuscript.

How should I ask my collaborator (foreign author) to include my supervisor's name as a third author? I need some help in this. 

**Edited:** As my supervisor has told me to add his name, I am obliged to add. I have no other options left. I am asking how should I write and request to my collaborator to include my supervisor name in the manuscript. Also, I am afraid whether my collaborator will feel odd or bad if I request him to do that.

Please help me: what should I say to my collaborator so that he may give third authorship to my supervisor?

Answer: 
Like many questions from graduate students, I believe a possible answer to "How should I write and request to my collaborator to include my supervisor's name in the manuscript?" is "Ask your supervisor.". 

The question to ask is something like this: "I'm about to write to Foreign Author to get your name added to the paper. What should I list as your main contributions to it?"

If the collaborator finds the result reasonably convincing, the supervisor's name gets added. If not, it is not your fault.
If I were your collaborator on this paper, I would refuse to add the supervisor's name no matter how you asked. The only reason I would consider adding it is if the supervisor had actually made a contribution commensurate with authorship (if that were the case, you should have mentioned this to your collaborator a lot earlier, rather than pretending that you had done the work).

One way of cutting the Gordian knot is to have your supervisor do some significant work on rewriting or expanding the paper. But, if I were your collaborator, I would need to be convinced that such rewriting/expanding would make the paper better.

And, by the way, your claim that your supervisor must be a co-author on every paper you write is utter nonsense. Any supervisor claiming this to be the case is acting unprofessionally and unethically.