And whence is it derived that He showed him the overturning of Sodom and Gemorah? From (Devarim, Ibid.) "and the plain," it being written elsewhere (of these cities, Genesis 19:25) "and He overturned these cities and all of the plain."
When the Torah Describes What Moses Saw from the Mountaintop, It
Mekhilta Tractate Amalek 2:28