The passage in question, Chapter 98 in Oathbringer:
“What were those two spren floating nearby, shaped as small slits in the air? They separated the sky, like wounds in skin, exposing a black field full of stars. When they moved, the substance of reality bent around them.
Szeth bowed his head. He no longer ascribed to spren any particular religious significance, but he could still be in awe of these. He might have lost this contest, but he seemed to have impressed the highspren.”