Midrash sa Deuteronomio 34:3: Mekhilta DeRabbi Yishmael & Shemot Rabbah

And whence is it derived that He showed him even the graves of the forefathers? From (Ibid. 3) "and the south," it being written of their graves that they are in the south, viz. (Numbers 13:12) "and they went up into the south and they came to Chevron" (where the forefathers are buried.)

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."

And whence is it derived that He showed him Gog and all of his hosts? From (Devarim, Ibid.) "the valley of Jericho, Gog and all of his hosts being destined to ascend and to fall in the valley of Jericho.