Tafsir of Al-Inshiqaq 84:3

Al-Dahhak said: It shall be flattened by the collapsing of its mountains and its hills, and by its leveling, until it becomes a smooth, level plain wherein you see no crookedness or unevenness.

Others said: It shall be increased in breadth and expansion, derived from "extended it" (maddahu) in the sense of "prolonged it" (amaddahu), meaning he increased it. Similar to this is the view that it shall be stretched, thereby increasing its flatness and enlarging its breadth.

Al-Hakim recorded, with a sound chain of narration from Jabir, from the Prophet (may Allah exalt him and grant him peace), that he said: "The earth shall be extended on the Day of Resurrection like the stretching of tanned leather, then the son of Adam shall have no more of it than the place of his two feet."