Isaac Asimov is a science fiction author (a good one, too), but the work he created was not a real description of our universe -- it was fiction, and playing with ideas.

There actually is a sextuple star system in the night sky. Castor looks like a single star but actually consists of three binary stars: two of them in a binary system that is itself in a binary system with the other binary star. I don't know if there could be a stable position for a planet that would never experience nights, but there is at least some reason behind the idea.

For stable, always day position, maybe the planet could be in L1 point between two suns?