"And We approached," meaning: We intended, "what they have done of deeds," meaning: good deeds, "and We rendered them as dust dispersed" in the Hereafter. Mujahid’s interpretation: It is the beam of light that enters through a window aperture.
Muhammad says: The singular of "haba'" is "haba'ah." "Haba'" is the scattered dust that rises from the hooves of horses, and it is derived from "hubwah," and "hubwah" means dust.