I'm frustrated with a mumbler
I see how they can be frustrating. Does he always do it?
he never seems to get to the point and he keeps repeating himself
It may be good to try and be more patient with people. This person may simply mumble because they are shy.
Because he has been talking for 3 minutes and he still hasn't said what he wants.
While it makes sense that this can be frustrating, just do your best to not get worked up. This is probably something that this person often has to overcome when they are speaking.