Musnad Ahmad 31:721

Hassan narrated to us, Ibn Lahi'ah narrated to us, Darraj narrated to us, from Abu al-Haytham, from Abu Sa'id, from the Messenger of Allah, may Allah bless him and grant him peace, that he said: "Wail is a valley in Hell, in which the disbeliever falls for forty autumns before he reaches its bottom. And al-Sa'ud is a mountain of fire, which he climbs for seventy autumns, then he falls from it likewise therein forever."