They grinned and went into the Neronian washroom, where a line of men bent over the bowls inset along a prodigious slab of marble as in religious prostration before their own images in the massy mirror.
There are no more uses of "prostrate" in the book.
Show samples from other sources
Francis chose to make it his cross to bear in life; he never understood why his Uncle Atticus remained on excellent but remote terms with his father—Francis thought Atticus should Do Something—or why his mother was not prostrate from his father’s eccentric, therefore unforgivable, behavior.
Harper Lee -- Go Set a Watchman
He sat down on the edge of the bed and softly kicked Colin’s prostrate body.