Sayyiduna Buraydah (may Allah be pleased with him) narrates this saying of the Prophet (peace and blessings be upon him): "If a stone were falling into Hell, it would not reach its bottom even in seventy years."
Al-Bazzar and al-Tabarani recorded it; the chain of both contains a narrator, Muhammad bin Aban al-Ju'fi, and he is da'if (weak).
Hadith Referenceمجمع الزوائد ومنبع الفوائد / كتاب صفة أهل النار / 18589