Where can I find in ancient texts references or descriptions of the smoothed surface of the ancient pyramids in egypt?
you can check here and here. a reference to the smoothness appears in an extract from Al-Masudi/Masoudi's "The Meadows of Gold and Mines of Gems".
from the first link, another reference to the smoothness appears in an excerpt from "Pyramidographia: A Description of the Pyramids in Egypt" by Prof. John Greaves.